It's called Swaptree. Have you heard of it?
See, normally I don't like to part with my books. But sometimes I need to make room on my bookshelf. Basically, I was able to get rid of A) my Twilight books, B) two awful adult fiction books, and C) any other lame miscellaneous books in good condition we have floating around. I mean, I was planning on just giving them away, but getting a book in return is so much better.
I've received Cry, the Beloved Country, And Then There Were None, "Henry IV", and A Separate Peace. I also got Eat, Pray, Love in a swap and after finishing it have been subsequently been able to trade it off as well.
It's magical how simple it is. You print the label and stick the book in the mail and get a book back.
So, try it.
Also, you should friend me. Sheepishsmirk.