LOL, nice site :D
Some of my favourites:
http://xkcd.com/c85.html - does anyone actually NOT do this??? lol
http://xkcd.com/c102.html - lol @ alt text
http://xkcd.com/c104.html - alt text on this is interesting to me, as I see psychopaths like terminators with egos ;D
http://xkcd.com/c129.html - scary!
http://xkcd.com/c6.html - Commonly known...?
http://xkcd.com/c124.html - LOL!
Actually I like too many of them to list... :D