Bookcrossing.com
This website is not designed specifically for book trading, but it is a nice side effect. The primary purpose of this site is to have people register books and then release them “into the wild” (such as leaving it in a coffee shop), and then seeing if someone finds the book. If someone finds the book, hopefully he or she will go to the Web site, enter the identification number, and note where it was found. That person can then release the book “into the wild” at another location. The idea is to see how far the book will travel (and track who is reading it). Although not dedicated to book trading like bookmooch.com, people can use it in a similar manner. Some people list books they have read and other people will read the reviews before requesting a “trade”.