So there's this great video game themed comic, Penny Arcade, that recently started hosting an annual expo. More so than a typical video game convention, this one is truly for the gamers, with video-game-oriented rap artists and rock bands, tournaments with classic Atari games, etc.
Apparently, it is also the world's highest concentration of geeky t-shirts, as documented by this flickr photo set. I think this one is my favorite. :D