Have you heard of Paperback Swap? If someone in your household loves to read, and you don't have a lot of money to spend on books this is a great way to get those books.
I use use Sonlight curriculum for my daughter. For those of you not familiar with Sonlight, it has a lot of reading involved. To save money I bought the Teachers manual used, and have been buying used or book swapping for the other books she needs. It does take more time, but the money saved is tremendous.
With paperback swap they will start off with 3 credits when you list 9 books. I easily had 9. Then after that you get a credit for every book you mail out. So, the more books listed the better your chances to get to mail out books. You use your credits to get books you want. They also give you an option to buy credits. I have done this once or twice, when I really needed some books for school.
With this being FREE (with the exception of mailing out books)it makes it a great resource for books. Oh and by the way all the books listed are not paperback.