A while ago, I made a sign for my door that reads "Architecture Help 5¢" (in homage to Lucy's psychiatry stand in Peanuts of course.) I get the occasional comment on it, so I decided to experiment and make a t-shirt out of it. These days, making your own t-shirt is cake with online services such as CafePress, T-Shirt Junky and Zazzle. I like Zazzle's pricing structure the best - they have a flat fee and pay you a royalty on sales. CafePress has a baseline fee and you can then charge whatever you want on top of that. I didn't want to be mucking around with pricing, so I went with Zazzle. Also, Zazzle has more choices and options for t-shirts than CafePress did.
My Zazzle gallery is named DevHawk Designs. So far, I have two products - the Architecture Help 5¢ shirt in black and in white, though Zazzle allows you to customize the shirt so you can get it on pink or navy blue if you really want it. I made it with Expression Graphic Designer, though it's such a simple design I'm sure I didn't really exercise its capabilities at all.
Other than me, I'm not sure who's going to buy one of these. Believe me, I have no vision of being the next ThinkGeek. But let me know what you think, good or bad.