I absolutely love Homeschool Classifieds. It is a great site for homeschoolers to buy and sell their used books for free! You can pay a minimal fee in order to list more than 5 books at a time, but it is more reasonable than e-bay. Not to mention, they also allow you to sell Teacher's Editions!! I mean, really, aren't those the books we're looking for the deals on or desiring to make some of our money back?
Check it out. You do not have to have an account in order to buy, only to sell. Let me know what you think!