With the start of my new, I have collected a small (~40) collection of t-shirts (most of the geeky sorts). A few people have asked me where I got them, thought I'd share.
http://www.tanga.com/products/relax-i-can-fix-it-t-shirt—9 << Daily Deal Site // Different T-Shirt every day
http://www.lolshirts.com << Most of mine came from here (Black Friday / Cyber Monday $5/$6 shipped!!)
http://shirt.woot.com/ << A few from here
http://www.thinkgeek.com/ << Have a couple from there
http://store.xkcd.com/ << Have one from here
I'm too cheap, but there are also some t-shirts from http://www.noisebot.com
For the NSFW shirts http://www.tshirthell.com/hell.shtml FANTASTIC place!!!
Good luck and enjoy!