Threadless

Threadless is an online community that produces and sells tee shirts.  They accept slogan and design ideas from anyone, you just have to use their templates and follow the guidelines when submitting.  Once you submit a tee shirt idea, it will be rated by the Threadless community.  If it ends up being made into a shirt, you'll get $2,000 and a $500 Threadless gift certificate, and the opportunity to make even more money if your design is reprinted.