Teesort.com

Teesort.com is another web site where you can earn money for designing t-shirts.  The site's guidelines aren't very specific; if your shirt design or slogan is selected, you could win "cash prizes," "a lifetime supply of T-shirts," and "royalty on each T-shirt sold."  You'll have to sign up for a free account in order to submit designs, and then your submissions are voted on by the site's visitors.