Threadless is possibly the OTHER best example of how community centered collaboration (That honor goes to Wikipedia) at the helm of web 2.0 is sparking new ideas and businesses especially in the E-Commerce front.
Members of the Threadless community (you can register to become a member) submit their t-shirt designs online and these designs are then subjected to a public vote. Designs that are popular (i.e. People like and would possibly buy them) are selected for printing and sold through their online store at www.threadless.com. Creators of the winning designs will receive a prize of cash and store credit. Basically, everyone wins.
A caveat though - The designs are printed in limited quantities (for all sizes) and the popular ones sell out quickly. If that happens, you can vote to have it reprinted and it enough votes are gathered (i.e. Enough people will buy the reprints), then that design will be reprinted.
These are 2 of my favourite Threadless T-shirts. And no, I don't have them yet because the size I want is perpetually sold out.
Fans of the old TV series would relate to this one, aptly titled "What would Macgyver do".
This one's called "The Beginning".