BookMooch.com is a huge (as in: 100,000’s of books), free, book swapping site. Why buy a new book when you can save one from the landfill?
It’s free to join and create your account. You start out by posting up some books which you are willing to give away. If someone would like one of your books, they request to “mooch” it from you. If you accept the mooch, you simply ship it to them paying the postage. In return you get a bookmooch “point”.
If you see a book you want, you can request to mooch it. (If the owner accepts, they ship it to you and they pay the postage.) Each mooch costs you one point. You earn points when someone mooches a book from you; you get 1 point for within-the-U.S. mooches, and 3 points if you’re willing to ship internationally. You also get 1/10 of a point for each book you list in your moochable inventory.