Are you like me and read a lot of books? If so you may like Swap.com (formerly known as Swaptree). It's a swapping program for your used books, CDs, DVDs and video games. I've been a member for about six months now and I love it.
Basically you list the items you are willing to swap and the items you are looking for on their website. Swap.com then matches you with someone who has the book you are looking for and wants one you are offering. Then you mail them your book and they mail you there's. It's as simple as that. Take a look here.