I use bookrenter.com. You end up saving way more money renting your books than if you buy them and then try to resell them to the school. And shipping it back to them is free because they provide prepaid shipping labels. If you use my referral link below, you also save an extra 5% on your purchase.
Rent Textbooks | Cheap College Textbook Rentals | BookRenter.com
And no i don't work for them, I just use them to rent all my books, and I also save a small percentage if people use the link. Its win win haha. But seriously, even if you don't use that particular site, unless you want to keep your textbooks for future reference, you should absolutely rent them. You save so much