PaperbackSwap.com – register for a free account and list 10 books you are willing to swap. That earns you two credits to request books from other members. The more your trade out the more books you get to request in. You pay to mail out books and receive them for free. The site is great for kid’s picture books and NY Times best-sellers. They also have DVD and CD swaps. Read more about how it works.
BookMooch.com – this site uses a similar system as PaperbackSwap. You pay to mail books and receive them for free. You need to send out one book for every three you receive to remain in good standing. BookMooch is free and has a very cute Web site.
Bookins.com – this site charges a flat fee of $4.50 per book but boasts better customer service than Paperback Swap and BookMooch. The site’s point system allows you to trade books for DVDs. You can also print postage from home. Read more about how Bookins works.
Goodwill and Salvation Army – large thrift stores often have a used book section. Expect older titles and great prices.
Your local library – but of course!
15 places to get free books online (affordable if you have a Kindle!)
Education World provides summer reading lists by grade (scroll down to see the options)
NY Times recommends these books for vicarious travel