Bookmooch.
Anybody who likes to read should know about bookmooch.com. It's a website where you can post books you want to give away, then earn points to request books from others. You pay postage on the books you mail, but I imagine it should even out in the end. I've already gotten rid of six books and received one, and two more are on their way to me. Awesome! The site is completely free (with no ads, even) and easy to use. I'm a fan.