This is a great idea, and has the potential to take off very quickly. One thing you might want to do is seed your site with a bunch of merchandise. Find an interested party with some cheap stuff to unload (like woot.com) and offer to help them move inventory.

You need to get scale first, and you need lots of sources before you'll get lots of products. At then end of the day you are selling affiliate revenue to website owners, so I would focus your message on that, and attempt to stuff the product pipeline with some choice partnerships, until you get enough affiliate sites to drive product.