Overspecialized Elves.
There's 8 billion unique subraces of elves, each with their own special powers. You have normal elves, barbaric elves, other barbaric elves, arctic elves, underwater elves, evil color-swapped subterranian elves, genius elves, winged elves, jungle elves, earth meditative rock elves, etc, etc, etc.
I'm sick to death of overspecialized elves. It's not like they're seperate cultures.. it's just a gimick. And you don't see this with other races.. just elves. You don't have 90 types of halfling running around. Or heaven forbid different stats for different 'subraces' of humans - that wouldn't be very PC would it.. but it's okay for elves. Pah.
All shash I say. Throw out the elven subraces, give elves 1 set of racial abilities and be done with it. If you want Drow, they don't have to be ECL 3, have magic resistance, and all manner of silly crap like that. Change their alignment, cultural facets and m.o and bam - scarey outcast underground elves that worship a demon queen.
... my other big pet peeve is monsters that don't make sense. Monsters that work quite well as a 'gotcha' when gaming, but outside of the game/dungeon context they don't make sense. Take the Rust Monster for example. Great dungeon critter, bane of adventurers everywhere.
Wouldn't live long at all. It eats oxidized metal, all well and good. And with it's feelers it can rust metal it finds for it to nosh on. Also fine. But the thing is, when it comes down to it, there's really only one easily accessable source of metal for rust monters to eat (unless they're always diving around in the earth looking for ore veins) - civilization. And given how damaging they can be to said civilization, they'd be exterminated activly once they were detected.