I've sold games (also movies, books, cds) through Amazon. If you search for the item, click "sell yours here", then list 1 cent under the lowest price you can almost guarantee yourself a quick sell.
Amazon needs credit card, gametz banned me for posting in the videogames trade area (i mean.. wtf?), Half and eBay doesn't allow MoneyBookers or e-Gold... gonna try Cheapassgamer now.