In the spirit of The 400 Project (which is a growing listing of 400 game design patterns), Sean Howard has started a site that will list 300 mechanics:
Every day for three hundred days, I will post a gameplay mechanic that has (hopefully) never been seen in a commercial video game. Three hundred mechanics. No more. No less.
Not all of them seem like game mechanics, but is sure is fun. Whenever I see these sort so projects I just so want to create a cross-media design patterns project. I’ve got so many to add already!
Check it out: http://www.squidi.net/three/sorted.php