Here are some of the best:
Best Geek Tattoos - includes gaming, pi (it's up to 80 digits), DNA, a ruler (NOT metric), and more.
Girl Tattoos - can't describe, just go to the link.
Girl Tattoos on the side - at least, these tattoos won't be marred by body changes as easily as the stomach tattoos.
These I DON'T suggest - on the foot - I've talked to students who've gotten them, and they say it's QUITE painful (apparently, if there is little underlying fat tissue, it's very painful).
Discover Magazine has 23 pages of science-y tattoos.