CafePress

www.cafepress.com
Unique visitors, January 2009: 4,665,000 (Nielsen Online)

CafePress lets you design and sell customized merchandise like t-shirts, posters, print-on-demand books, and CDs.

Pros: CafePresss on-demand production means no unsold inventory.
Cons: You can only customize items the site already offers, not sell your own products.

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