As any college student knows, textbooks can be extremely expensive. And when you've finished a course, you may not need or want that $100 science book anymore. Why not avoid buying and selling back altogether by renting? Check out Chegg.com, which allows you to rent books for a fee that is typically much cheaper price than buying. If you prefer to purchase or decide you want to hang on to your rental, the site allows buying and sell-backs. BookRenter.com is another rental-based site, and TextSwap is a user-to-user book exchange system.