A great way to earn some extra money is by selling your used books online. You can go to
www.ckybooks.com and simply enter the ISBNs of the books you would like to sell, you will get an offer for each book (unlike some stores that make an offer on the entire lot) which you can choose whether or not to accept. You then ship the books free of charge to the company. When the books are received, payment is sent by Paypal or check, whichever you prefer. It's very easy and the website guides you through each step.
Keely