Swappingtons lists “all sorts of books, CDs and DVDs that other folks own, but wish to swap away. The way it works is simple: You list items that you don’t want, and someone will swap you for those items. When they swap you, they transfer swap points to your account, and you mail them the item in question. Once you have the points, you can go and spend them on other items that other folks list on the site.” (Link found on Crabwalk.)
Incidentally, if you’re inclined to list someone as the referring user, and that someone is me, my user name is maudnewton.