If you like to own books and share them, try this paperback sharing site: Paperback Swap. Members lists and mail books to each other for free. The mailing person pays the postage and gets "points" in exchange. Here is the explanation for how the site works:
"List at least 9 or more books in the system to become an active member and receive 3 free credits to get you started trading. List as many books as possible to be more successful in trading.
Browse our online list of books posted by club members, and use your credits to order books.
Selected books are delivered right to your mailbox, for free!
When other members order books that you’ve listed, you mail them from your mailbox and you pay the postage (usually $1.59).
You get one credit (good for one book) for every book you mail when it is received by the club member who requested it.
List as many books as you like. The more books you mail to other members, the more credits you'll receive. "