I am working on de-junking my house and storage unit. A few weeks ago I brought all of my books home from the storage unit and was searching online for a way to sell them other than half.com and amazon.com. What I found was a great site, Cash4Books. Cash4Books is super easy to use and fast. All you do is enter the ISBN number from the back of your book. You will get a message letting you know whether or not they are buying that book. If they are buying, it will tell you how much they will buy the book for. Once you have books in your seller cart, you check out, and print the mailing label. Shipping is FREE!!! Cash4Books will send you an e-mail when they receive your shipment and another when they mail your check. Today I received my check for $14.00. They weren't buying a lot of my books (I think they bought 9) but I am not complaining. This is $14 I wouldn't have had. The rest of my collection has been donated to the library.
If you have books that you are looking to sell, this is the place to start. I have used half.com but between the shipping costs and the fee you pay to the site for selling them, I found it wasn't really worth my time and I didn't see a very good return.