Goozex
When I have a really good experience with something I'm going to write about it. No question whatsoever. Jim told me about this site called Goozex which is a peer to peer game trading site.
Here is how it works. Lets say you have about 10 games you no longer play and you don't want to get the crappy trade in values that certain game stores give you. Well, you to Goozex, post your games in "Your Library" section. Now from there you will see what the point value of the game is; they don't use a dollar value. You will also see your turn. The turn is your place in line to trade your game.
Once it's time to trade your game, Goozex sends an e-mail to both you and the buyer indicating that a match has been made. Goozex provides address information, etc. You mail it off, then wait for your positive feedback. In the beginning of your account you need positive feedback to get your points. After a few trades you don't have to wait.
Once you have points, you need to pick up trade credits which are a buck a trade and sell in blocks of 5. Now pick your game, wait in line. Now you may say "Hey! I'm in the 50th spot, well that may not hold true because the people ahead of you may not have credits or points and they will be skipped. But this is REALLY cool, I have no complaints, this is something to check out.
By the way my first trade was for "Halo 2" for 300 points, which equates to $15 bucks! How can you not go wrong. But do research on the game you want, and make sure you're getting the deal.