If you love books, then chances are you have many bookshelves in your house that are collecting dust. Yet the urge to buy more books tugs at your heart, and you realize that you have no more room to bring home new ones.
The websites below will solve that problem. You can either turn old books into useful things, or simply trade them up for ones that you want to read.
Book Mooch

This is a great way to exchange books. It is easy and simple. Sign up, list your books, receive requests for your books, mail out your books, earn points, and trade your points for new books. This site also offers books in Deutsch, Español, Français, Italiano, and Português languages.
Paper Back Swap

Similar to Book Mooch, you will need to register, list your books, receive points, and turn your points in to request for other books that you want. Membership is free, but may change as it gets more popular.
Beside books, Paper Back Swap's sisters sites are Swap a CD and Swap a DVD.
Bookins

Sign up for free membership, create your list for trading, and select what you want. You can also include DVDs, and exchange for other playable DVDs. This is a brilliant way to get books and DVDs that you want! You can then decide to keep them or circulate them again.
Book Crossing

This is a unique book club! Sign up, and list your books using BCID numbers. Instead of mailing your books, you simply leave them at places you go. For example, you can leave a book at a coffee shop, a park bench, train station, the gym, or post office, and let destiny decides its faith.
Book Crossing is hoping to bring literacy all over the world, and it has more than four million books registered with 687,481 members.
Make Useful Things

Although cutting into a book is not my favorite thing to do, this site offers many useful things you can do with your old books. You can make a holder for your iPod, bookends, child's flap book, table legs, clock, and lamp shade.
This is such a wonderful way to exchange old books, or make uses of them. Personally, I like Book Crossing's idea of leaving the book for other to find. It will be interesting to track down where my books travel to.