BookCrossing.com offers a way to recycle/share books. By registering your book through the BookCrossing website you can track the "adventures" your book takes. Leave your book on a park bench, coffee shop, hotel, or anywhere someone might find it. Then log on to track it as it globally passes from person to person. Each book has a unique ID number so future readers can log on and see where the book has been. You can even leave comments about what you thought of the book.
Lately I've been contemplating ways to purge my bookshelf and this seems like a great way to pass on good reads in an eco friendly manner.