I have been trying to figure out what to do with my Xbox 360 games after I finished them. I have been selling games back to GameStop, but the amount of money that you get is pretty low. My friends recommended that I try Goozex.
Goozex is a site that you can trade your games for points, and you can use those points to get other used games. Goozex sets the point value for the games. You can list your games, and then when your offer gets to the top of the list, you print out a label and send the game directly to the person who requested it. When they receive it, they acknowledge it, and you get credited for the trade.
The main benefit of Goozex over GameStop or Amazon Video Game Trade, is that the value of the any game that you trade, is a lot higher. You can actually get a game by trading a single game. With GameStop or Amazon, it is very unlikely that you can get a recent game after a single trade.