Bookmooch sounds like what you want.
List your books, you get I think 1/10th of a point per book listed & a point per book given, use your points to request books others have listed.
Looking at my profile I've had 84 books off there & given 68, must admit I haven't used it for a while and I need to update my list of books available to be "mooched".
You can get (& give) books overseas as well, it just costs more points.
Also, you can add "friends" so if people post their user names up, people can add them as friends and see what is being shared by STW members.
My "inventory" of books available to swap is here