"You simply list the items you have and the items you want, and Swaptree's trade algorithms, instantly finds the members who want what you have and have what you want. So on Swaptree one copy of Harry Potter The Deathly Hallows, can be traded to another member, and another, and another, saving trees and pollution in the process. After all do we really need 40 million copies of Harry Potter on the planet? Shouldn't say 5 million be enough? Lets recycle all the paper AND all the books."
just signed up on this site, and it's great. it's free to list items you have and want, and the only price is postage. and you don't even need to go to the post office--swaptree will print your postage and mailing labels for you, so all you have to do is print, put your item in the envelope, and put it in the mailbox. it's like getting brand new books, music, movies, and games for around $2.50 no matter what they are!
or, the site can even match you up with people who live near you or go to your college, so you can swap by hand for free.
[more at swaptree.com]