There's one site I know of (because I help run it) called Video Game Evolution www.vgevo.com that has it's own Classifieds/Auction/For Sale/Trade section that works close to the way eBay works, but without the horrible "take a cut off the profits" fees. You can use online credits to list items, and the community has been good about getting items to people, making it a seemless, "nearly" painless process.
It's small, but it's growing. I wanted to help start it for gamers b/c of all the jerky BS of eBay. Wish me luck!