A friend of mine referred me to this fantastic site the other day - Paperback Swap - a book swapping/trading website. Basically, you list books that you no longer want and get credit each time someone takes one of your books. Then you can pick a book from the millions that are listed. You pay the shipping when your books go out, the lister pays the shipping when you choose a book. A great way to get some really inexpensive books (just the cost of media mail shipping)! And it's a great way to do a little de-cluttering.
***If you decide to give it a try, I'd appreciate it if you'd list me as your referral (firstname.lastname@example.org) Thanks!***