Zazzle.com does custom shirts and other stuff with no minimums, and has the best interface I've ever seen for creating and refining new artwork.

Also, I've so far been really impressed with the quality of their wearables, and they have a 100% customer satisfaction guarantee even on their custom printed materials.

Their printing is some sort of patented process that isn't a crappy transfer, and they claim it's as durable as conventional screen printing.

I have limited experience with them but so far have been very happy. Even their return process is simple.

I don't think they do stuff that's blatantly adult but if there's no nudity they would probably be fine with it.