A new pixel-art t-shirt design challenge will open soon at Threadless. Let's do this, PJ!
However before you rush to post your fave pixel pieces, take the time to think hard about what makes a good t-shirt design, as opposed to a good piece of art (pixel or otherwise). Great shirt designs usually have a strong underlying concept, and make use of the shirt background color as a prominent design element. Beware of boxy (rectangular) designs that don't have a good reason for boxyness (such as fake film posters, comics pages etc).
The challenge opens a week from today, and should last for 2 more weeks. You can already ask for feedback on the Threadless forums. Trigger warning: it can be a tough crowd to please out there!
Also be aware that chances of print are very slim, well under 1%. Do this as a chance to compete and improve, not to make easy money. Now pixel away!