Reader Kelsey Elliot has suggested the site MyBookBuyer.com. She says:
For years I've been using a service called MyBookBuyer.com. It's a place were you can sell all of your old books online, and they pay for the shipping. Convenient right? It has been a great way for me to get some extra money at the end of the semester, and I don't have to deal with long buyback lines.