I found this great site, PixelTees, where you can design your own (pixelated) shirts and sell them - or just make them for fun.
Here's my first, very simple design.
Which gives me an idea. Sponsor me for blogathon and I'll make a shirt especially for you. I'll be making them and showing them off for all the people who sponsored me already. There will be a different saying and/or picture for each sponsor, chosen at my discretion.
Ah, another great time waster.