If you've never been to threadless.com, (disclaimer - this link uses a referral system to credit me if you buy) check them out. They're an ongoing t-shirt design competition, with limited runs of the shirts. Popular ones get reprinted. One of the designs I like a alot, spoilt, has been reprinted:

If you get on their email list, you'll get the new designs every Monday. Occasionally there'll be some I like, and even less occasionally one I'd actually wear.