I joined this site a few years ago, and have love-love-loved it from Day 1. If you're looking for some good summer reading, check it out ASAP! As of the time of this post, they have OVER 4 MILLION books to choose from!! Yes, you read that right! And you get 2 free credits just for joining and listing 10 books that are gathering dust on your shelves!
If you haven't yet checked it out, I can't recommend it enough! So far, I have traded 147 books and all for free! You pay shipping to mail out your books to those who request them (usually no more than $3 - can you buy the latest book for that? I think not!) When you request a book from someone else, they pay shipping to mail them to you....what a great system! You get credits for each book that you send out, which you then use to request books you want from other members.
Oh yeah, they also have audio books (2 credits) which is my current favorite due to time constraints. I order a couple at a time and always have something good to listen to on my commute to work & back. :)