Jayren's list is good, I'll add a few to that:

http://www.triv.net - Lots of quizzes, in the style of "Who wants to be a millionaire" (except you don't win any money unfortunately). They have them on almost every subject imaginable though, fun.

http://www.desktoppoetry.com - Just like fridge poetry! Yay!

http://www.ebaumsworld.com - Funny stuff.