Swaptree is a free service that allows you to swap books, DVDs, music CDs, and video games. They match you up with people look to make swaps and alert you to swaps that are available. Once all the parties agree, you mail out the stuff you are trading, and you get the stuff you are trading for. I've been using this service for quite a while, and all the people I've dealt with are legit... I haven't had any problems with things not showing up.