If you have accumulated as many books as I have...

You may be interested in a book swapping site such as BookMooch.  On this site, each user gets fractions of points for each book they enter into their inventory.  Then, when they have sufficient points, they may request a book from another user for which they will pay 1 point and the owner of the book will receive 1 point (slightly different for out-of-country mooches).  The owner of the book pays the postage to send the book to the moocher, but now has an additional point with which to mooch a book for himself.  Each user can build up a wishlist of books they would like to have and an email will be sent when one becomes available

It's a great way to clear off your shelves and get some new books to read at the same time.  The only cost is the postage for sending books to other users, and if you use Media Mail, the cost is usually just over $2.  Where else can you get books for $2?

There are other book swapping sites, but I like BookMooch best.