PaperBack Swap

Mail a book. Get a book. Any book you request is yours to keep, share or trade. No late fees. No processing charges. No hidden charges. Every time you mail a book to another member, you can request one for yourself from over 3 Million.
http://www.paperbackswap.com
While you’re at it, you can register at their sister sites for CD and DVD (SwapaCD.com & SwapaDVD.com). You can swap your unwanted CDs and DVDs for new-to-you ones, and you can also transfer credits between your accounts at each site – so you can turn CDs into books, books into DVDs, etc.
Thanks, Money Saving Mom!