Books Books Books!
I stumbled upon this web-site that I think is completely awesome and anyone who enjoys reading but hates to spend money will agree.
It is free to join for at least the first year (they mentioned possibly charging a $10-$20 annual fee but you are guaranteed at least the first year free) and you post books that you no longer need/want. When someone requests a book from you you have to ship it at your own expense which kinda sucks. But, in return you get one book credit and can get a book sent to you on that person's dime. To get a book it costs 1 credit.
See how that works out?
Also, when you register and post at least 10 books to share you get 2 free credits. You can also buy credits for something like $3.
50 a book but why do that when you can get them for free?
Anyway, here is the link.
If you sign up through this referral link I get an extra book credit for it and I like that a lot!