i have the pacman level 256 t-shirt from errorware, it's really interesting looking i think.
amongst my other favourite geek-chic t-shirts are:
Horace Goes Skiing
2x Sensi Soccer
and a Gauntlet one i cant find a picture of online...
i was going to get the Guru Meditation one, but its a bit too simple a design to bother ordering it from there when i could probably get it made up myself. (which would mean i could also pick my own error number!)
It is damn cool though! (as is the Gauntlet "you are full of bombs and / or keys" one.)