I know most people have heard of Threadless, but Naked & Angry, another skinnyCorp company, is lesser known. Here instead of t-shirts, you submit patterns for judging and scoring by users of the site. Then if ranked high enough, they will be made into products such as wallpaper and neckties.
Currently they have 5 wallpaper patterns and 5 neckties available for sale. The turnaround time is much slower than Threadless. But according to this recent Inc. article, they plan on revamping the site soon by expanding the product range to include handbags, wallets, and dinnerware, with a new product launched each month.
They also have a great blog (although it hasn’t been updated in awhile) about patterns and pattern design.