I haven't posted recently because I have been busy elsewhere. A sword and sorcery setting for Gamma World, reading Clark Ashton Smith and thinking about a multiverse very different from the standard in D&D (the wheel and the 4th edition versions)- one that does not include the afterlife as planes and some critter ideas that I will be posting some time in the future. But right now I want to show you a new pdf from Sean K Reynolds entitled File of the Serial Numbers: http://www.rpgnow.com/product/114214/File-Off-the-Serial-Numbers
At first I didn't pay much attention to it because I thought it was reskinning monsters to make new monsters. That is an old idea and I have plenty of sources on it. No, FotSN is on using creature stat blocks for humanoid NPCs. That is a nifty idea that should cut down the time to make new characters by a hell of a lot. It has suggestion on what to leave and what to change. The first example is using a hound archon stats for a paladin. Some of its abilities, especially teleport at will, could be dropped or represented by a class, magic item or something else. The players will have no idea and may want to dig and find out. Another example is using the barghest's stats for a cultist. Now that is a pretty awesome idea. Cultists can get all kinds of weird powers because of their patrons and the tests and rites to prove their worth. The feeding ability may be dropped or it could be used to represent a cult that worship a cannibal god or demon, one that allows them to grow stronger with the more people they eat. The most common things to change for most creatures are type and size.
Even if you don't want to use the stats as is, the number of monsters with unique abilities is staggering (thousands in d20 alone and then consider other games). These abilities could be used to enhance encounters with people, people who may not be quite human(oid) any more. Considering all the magical things the PCs encounter, they may very well become such people...
There are two other sources that I know of for this kind of thing. Bastion's Spells and Magic had potions that could provide powers of creatures, but at great cost. I think those costs, or possibly water down versions, could also help make encounters memorable. The other is Distant Horizon Games' Distinctions and Demerits. That covers a lot more than strange powers, from contacts to enemies, but it does include some ideas for curses and powers that PCs will get from their actions.
In any case, think about all the other sources you have on hand to help in designing the most interesting NPCs you can. What kind of freaky character can you make from the stats of a young green dragon?