TBS has put together a TBS Department of Humor Analysis where you can help them in their research of what is truly funny.
My favorite is the Survey where you can watch a clip from "Seinfeld" in any language you choose (I chose Mountain-style...hilarious). You then must determine which is funnier.
I also enjoyed making desktop wallpaper of a bunch of bananas. (Took a while to process, though.)
[Thanks to pixie for directing me to it!]