Here is a really cool site that allows you to swap books.
Paperback Swap help readers share their books online. You can list books you'd like to swap with other club members. Once a book is requested, you then mail it to the club member. In return, you can choose from 1,848,017 available books!
You pay the postage fees for the books you send out and the books you receive come to you postage paid. And the best part, the books that you request are yours to keep, or swap again!