As I mentioned a while ago, I think that 3.X/d20 feats would make a great resource for magic items for OSR games. While I was reading through several of my books and pdfs, I decided to concentrate on feats for classes other than magic-users. Metamagic feats are in profusion and most of them are easy to use in this fashion. So here are some ideas for the other classes or all classes (by source). Some are not converted- I like the basic idea and took it in a different direction. Keep in mind that some of these are meant for specific classes. Only those classes can use these items at all (or to their potential for weapons).

The XPH has a bunch but three caught my eye.

Rapid Metabolism can be used in a few ways- in the form of armor, a ring or amulet. It is weaker than a Ring of Regeneration in that is just doubles or triples the normal healing rate. But it also affects damage taken when the item was not worn.

Return Shot is used on shields or bracers and allows the wielder to reflect ranged weapons. The basic version works on arrows, darts, etc. A more powerful version works on siege weapon ammo and rocks thrown by giants.

Up The Walls is weaker (and thus cheaper) than a pair of Slippers of Spider Climb and allow the wearer to run up walls and across ceilings. Stop on any non-horizontal surface and fall (or grab on if you can). Handy for thieves looking for a quick escape from the watch. Can be added to Boots of Speed.

Dreamscarred's Untapped Potential is a psionics supplement with a lot of useful feats as well as one new kind of feat that has potential.

Course Correction allows someone to alter direction in mid jump (even backwards). This is another item meant for thieves.

Falling With Style is used for boots and allow the character falling to always land on their feet and damage is reduced by 30' worth.

Focused Dreamer provides a bonus to saves versus psionics, enchantments and other mental attacks while the character is asleep. This should be a pillow or blanket.

On Fire is a weapon enchantment. If the wielder gets two 20s in a row, the weapon's +1 increases to a +5 until it misses.

Psychokinetic Fists becomes gloves for monks. They allow the character to strike an opponent from a distance. There are three kinds- 10', 25' and 100'.

Vigilance of the Giants becomes head wear or bracers. It allows the character to act in a suprise round.

The mantra feat, in UP, gives a focused character an ongoing ability for a few minutes. It can be ended early by discharging for a more powerful effect. This can be used for a wide array of items, but I would allow the weak power to be constant and the recharge time for the weaker power to return is between one hour and one day (or longer for artifacts). An example would be a Sword of Lightning. It does an additional 1 point of electrical damage per hit and can be used to throw a 30' long bolt that does 3d6 points of damage. It takes an hour before the sword recharges.

Genjitsu's Metablades, Expanded Edition is a psionics and magic supplement (combining them with martial ability).

Shimmering Strike applies the Blur spell to a weapon. Because it is so hard to see, the target loses their armor class modifier from dexterity.

Spellstrike is used on ammo. It allows a spellcaster to imbue a spell into the weapon, it being discharged when the ammo hits (the target or the ground). Spells like Lightning Bolt and Cone of Cold start at the point of impact and then randomly extend from there (use the grenade miss chart).

Supernatural Familiar is armor used for animals. They can be familiars, druid or ranger allies or trained warbeasts. The item turns them incorporeal and allow them to attack freely with corporeal weapons. Ghost Touch might be a good thing to incorporate if you plan on using this.

Otherverse released some d20 Modern pdfs with some nifty (and some rather gruesome) feats. Here are three, the first two from Cruel Evolution and the last from Sexually Transmitted Future (about genetic engineering).

Disease Friend becomes vestments or head wear for clerics. It allows the character to speak to diseases, potentially causing them to leave a victim, go into remission for a time or become stronger.

Clobber is a weapon power and meant for fighters. It causes causes knock back and knock down. The weak version sends the target 10' (adding d6 points of damage) and the strong send them 50' (and adds 5d6). Those hit can save to avoid be thrown but are still knocked down.

Discriminatory Scent becomes a mask for rangers, paladins, druids and clerics. It allows the wearer to smell everything about a target- fear, what they last ate, race, if they have or used spell components recently, etc. For rangers, it provides a bonus to tracking. For druids, it helps when searching for specific plants or animals. Paladins and clerics use it to root out heresy or enemies.

AEG's Wilds has a lot of feats, several that can be used for magic-users. Here are some of the others:

Branch Runner converts to a pair of gloves that can be used by druids and rangers. They can climb trees without a chance for falling and move through the canopy at full speed as long as the branches are no more than 10' apart.

Dunesliding are used for boots and allow surfing or skating on sand, snow and ice. The wearer will not fall and increases their speed by 50%.

Flotsom is used on armor. The wearer floats and looks like a log or other vegetation as long as they remain in the water (they can swim).

Footman's Nap is used on a saddle and allows a rider to sleep while riding. This includes rest for spell memorization.

Listen to the Whisper of the Forest is head wear for druids and rangers. They can understand plants and will know if there are any plant creatures nearby. It does not give them the ability to talk to the plants.

Pit Fighter's Introduction is a shield power that can be used by fighters, rangers and paladins only. If there are two or more enemies within melee range, once per round, the fighter can redirect a missed melee attack against them to hit the other enemy. The initial attack roll is still used and damage, if any, is normal.

Rock Throwing becomes gloves that allow the wearer to throw stones and bullets, in effect a sling. This can be combined with other magical sling powers. In the hands of a halfling, the damage increases one die size.

Snake Handler is another pair of gloves. They allow the wearer to throw small animals like darts. It is meant to be used with snakes, spiders, scorpions and other venomous animals, but any very small animal can be thrown. Drow and other vermin allies gain +2 to damage when using arachnids and insectoids. Lizardmen, troglodytes and other reptile people gain +2 to damage when throwing snakes and other reptiles.

Tree Sleeper is used for armor or blankets. It allows the user to sleep at any angle or on any non-hazardous surface (so on a mountain side but not on thin ice).

Distant Horizon has a few books with handy feats. The first three are from The Practical Enchanter and the second three from Legends of High Fantasy.

Exorcist is applied to holy symbols and alters how turning works. Instead of rolling on the chart, the cleric does d4 points of damage per level to all undead within 30'. The creatures may save versus spells for half damage.

Merchant is converted to a ring or clothing and allows the wearer to sell anything at 95% of full price to any friendly character. Of course the buyer still has to have the money to spend.

X-slayer is applied to weapons for thieves. It allows backstabbing to damage creatures that are normally immune (like undead, elementals and oozes).

Quarterstaff Master is for fighters and magic-users. It gives them +3 to hit, damage and -3 to armor class.

Sea Legs are footwear that allows the wearer to ignore rocking motions and sea sickness.

Skull Totems are made from the skulls of enemies. As long as the skulls are on display, they hum and provide a triple strength Prayer spell. They are still bone and can be destroyed as such.

Epidemic Books have revived the Oathbound setting with Oathbound Seven. It has a few feats that could be used as magic items.

Blistering Flash is used on weapons and shields and only fighters can use the enchantment. In bright light, the wielder can reflect light, blinding and burning an enemy within 10'. A failed save versus wands results in d6 points of damage and blindness for 2d4 rounds.

Evolve is a torc, helmet, armor or cloak and allows the character to take levels in a different race. So a human fighter can multiclass to dwarf or elf with this magic item and slowly transform as levels are earned. Or, if you want, it could be to lizardman (Mayfair had a decent supplement for them back in the 90's), ogre, gnoll, displacer beast or whatever else the LL is willing to try. Removing the item simply stops the ability, it does not cause the wearer to revert to their original race.

Sand Surf is applied to a kite or clothing. It allows the user to windsurf on a variety of surfaces, increasing their speed to 75% that of the wind.

Somnambulant is applied to clothing, armor and bracers. It allows the character to sleep walk and fight. They take -4 to hit and move at 50% normal.

Weathered Archer is for fighters and rangers (obviously as a bow) and allows them to ignore wind and other bad weather.

In the 3.0 Masters of the Wild, there are the X Toughness feats. Each provides 5, 9 or 12 hit points. I would use them for rings, armor and cloaks.

Savage Species has a few feats. Monstrous feats aren't that special in that they don't change the user that much.

Cumbersome Reflexes is used for armor. When the wearer is exposed to an area of effect attack (spells, explosives, dragon breath weapons, etc.), the armor freaks out and bounces all over the place. It adds a +4 to the saving throw but does the wearer d4 points of damage as well. The other Cumbersome X feats can be applied to armor and have similar effects.

Detach is applied to torcs and headware. It allows the wearer to ignore vorpal attacks (they simply can not be decapitated) and once per day, the wearer can remove their head for a maximum of a turn (10 minutes). If the head is not back on the neck by then, the person dies.

Fling Enemy is converted to gloves. If the owner can actually lift another creature, the gloves allow that creature to be thrown as a sling stone (obviously after being grappled). Falling damage does apply for the distance thrown, both to the creature thrown and anything it hits.

Prehensile Tail is converted as a cloak. It isn't an actual tail, more like Spawn's shroud. It can be used as a weapon, and does damage as a short sword, used as a hand or to grab onto a surface and prevent falling. The cloak can hold up to 500 pounds but this weight is added to the wearer's encumbrance.

Thunderclap is used on gloves, gauntlets and bracers. It allows the wearer to paralyze those within a 30' long by 10' wide cone. Those failing their save are paralyzed and prone for d4 rounds.

If you want some magic items that do change the user, potentially for use with Realms of Crawling Chaos or the D series of AD&D modules, Lords of Madness has Aberrant feats. Putting on or using one of these items causes a horrific transformation that can only be reversed with Remove Curse or better spells. Until then, the magic item is a part of the character. People will see the transformed as a monster, something much more vile than a simple orc or even an owlbear. The reason people use these items is simple- they are very powerful and there is a well known cure.

Aberration Blood is turned into a variety of magic items, usually masks but anything is possible. They alter the user so that monsters will see them as kin. Brain lashers, chimeras, evil dragons, eyes of terror, gargoyles, gorgons, hydras, lamias and similar creatures will see them as kin, allies or "not food" as the case may be. Each creature has its own magic item(s). And yes, there is also a version that allows such creatures to hide among humans and demi-humans.

Inhuman Reach is always converted as bracers and adds 3 to 5 extra joins and sections of limbs to the user's arms and provides an additional 10' reach. Climbing is much easier. Thieves gain 30% and non-thieves can climb as if they were 3rd level thieves. Some (10%) add an additional pair of hands. They produce Y shaped arms with the additional joins and sections. These additional arms can be used in combat but suffer a -4 to hit. Most people use them to hold shields (so up to 3 shields) or other objects.

Starspawn are cloaks that turn into ragged, slimy wings that provide flight equal to 150% the land speed of the user. It also alters the wearer's skin, giving them a +2 to saves versus cold attacks and immunity to natural cold conditions. The character turns a sickly green with black and yellow markings.

Waterspawn is a cloak or armor that turns the wearer into a Medium (or whatever size the wearer is) sea serpent. Limbs are lost, swim speed is 200% that of the land speed of the user and they gain a poisonous bite (class 16, page 143 in the AEC).

Portals and Planes, from FFG, has a few feats that make handy magic items.

Dimensional Sense becomes head wear or an amulet. When someone or thing teleports, plane shifts or astral projects and arrives within 50' of the wearer, the item gives a one round warning.

Watchful Strategist becomes goggles or a helmet. After watching an opponent for 2 rounds, the owner can determine class, spells, psionic powers, special traits and abilities. Basically the player has access to the monster or NPC's sheet.

Well-timed Strike becomes a weapon that can be used to automatically parry any melee attack. It can only be used to its full potential by fighters and paladins.

Distant Horizon's Eclipse has many, many feats (and feat trees). I am going to stick to those with abilities that can make very different magic items from those in LL/AEC.

Spirit Weapon is a glove, gauntlet or bracer that summons a weapon made of energy. It does double damage of the normal weapon. But as the weapon is made from fire, lightning, etc., those resistant or immune take less or ignore the weapon. A more powerful version allows the wielder to throw bolts of that energy (treat it as a short bow and does 2d6 points of damage). A variant makes changes the visual of the weapon. For example it may look like a chain made of ice but it actually is a longsword made of fire.

Equipage is a bag or other container that allows the owner to reach in and pull out non-magical items. Anything worth less than 1 gp can be taken once per round. To get more valuable items, the user can dump money or other valuables (not stuff taken from it) into the container to pay for the resulting item. So need a long sword? Give the container 10 gp and it spits out the weapon. Of course the size of the mouth of the container will limit what can and can not be bought this way (no psychic tandem war elephants from a box 10 inches square).

Assistant is usually gloves, armor or tools. It allows "aid another" type actions. This means in combat, the user could give up their attack to give another a +3 to hit (a variant item would add only to damage or to both).

Blood Curse is a weapon. If it hits a spellcaster or magic using monster, the target must save versus spells. Failure means it can not use such powers for 2d4 rounds. A powerful version can even suppress a dragon's breath weapon.

Though Body Fuel is mostly for spellcasters, it could be added to magic items so that they can be used in Anti-magic Fields. This costs the wielder 1 hit point per round that the magic is sustained.

Companion is converted as a magic item for animals and monsters. It gives them -2 AC, +2 to hit and an additional hit die. More expensive versions make the creature larger, allow it to shapeshift and even take weapon and armor powers.

Dominion is a throne or even a building. The owner gains control over many people. Think of it as a pumped up version of the Leadership feat, but instead of dozens, it allows control over thousands or even millions. The people can rebel but it takes a save versus spells at a -6 penalty to even have such thoughts, much less actions.

Immunity is a long, involved feat as it can be immunity to anything. Of course armor that provides immunity to weapons will be very costly (and difficult to take of of its current owner). It can be turned into huge array of magic items. They could ignore encumbrance (Nodwick must have one of these); poison; disease; a specific spell, school or sphere; falling damage; lack of air, food or water; negative energy; breath weapons; enemy concealment or cover; aging; being transformed into undead or other monster type; etc. Of course many of these items may provide resistance instead of immunity.

Mentor can be converted to a little crystal ball. It allows two way communication between two specific people. Usually, this is a way of getting advice or calling for help.

Occult Sense means infravision, ultravision, darkvision, blindsense, tremorsense and anything else you can think of. Usually it is head ware, gloves or boots (for tremorsense).

Occult Skill provides magical abilities that are not quite spellcasting. The book gives the examples of alchemy, navigating dreams and eating people and monsters for their powers. This would be a book, scroll or other form of writing. I also suggest taking a look at the rules for Incantations in Unearthed Arcana and Urban Arcana (they are slightly different) for other ideas.

It also has weapon proficiencies that are non-standard- biological attacks (vermin and diseases), gases, psychological and a few others.

And it has martial arts powers that might be handy in customizing monks (swapping out their existing class abilities).

And one other thing. I was looking through Giant Lore for feats and none made me think of new magic items (for PCs). One did remind me of the Mattock of the Titans and I think would make a useful additional power for that item. It can be used to hit the ground and displace soil or loose stone, forming a 4' deep pit 10' in diameter and a mound of the same size within 5' of the edge of the pit. What this does is allows the giant to make the ground too difficult for charges. Considering how much damage a lance can do to them from the back of a charging warhorse, this is a power that might be common in the hands of fire and frost giant weapons as well as mattocks.