Perhaps not the most overused concept ever, but one I'm wearing thin of is vampires. Every goddamned time somebody writing anything wants to make a character "dark" and "mysterious" and "aloof" and "supernatural" and "hawt" and don't have fucking night elves in their setting, they go to vampires.
Every.
Goddamned.
Time.
Now, maybe it is because I play Magic, or because got my hands on my dad's old AD&D books at a relatively young age, or or because I got my ass into a library at a younger age still, but I know for a fact that there are well over a dozen different types of undead, ranging in a whole spectrum of exciting flavors. Liches, for example, are a good example of intelligent undead that could serve as a main villain, and I cite Order Of The Stick for precedence.
Why yes I am complaining about stuff I don't like, that is why I'm complaining about them.