They also donate money to and support causes for literacy including Invisible Children, Room to Read, NCFL, Books for Africa, and World Fund, which are all non-profit organizations. I just bought a few used books and sold a couple textbooks to them today. They are really friendly and have a great selection of books. While donating and buying used books you will also be helping stop pollution by recycling, reusing, and saving room in landfills!!
http://www.betterworldbooks.com/