You could try http://www.half.ebay.com/, or you can use http://bookscouter.com/. Book Scouter finds the website that will buy your book immediately at the highest price. I use both of these websites but I usually find that the websites through Book Scouter are only willing to pay about 1/2 of what you could get using half.com. Another way to sell books is at your college campus bookstore, just make sure that the books that you want to sell them are the ones that they are currently selling to students otherwise they will probably not take them. You could also post ads for your books around the campus (with permission from the college first). Good luck!
I would suggest using GreenTextbooks.orgSave Money, Save The Planet GreenTextbooks.org specializes in the recycling of textbooks, DVDs, CDs. Buying used textbooks not only saves you money, but cuts down on greenhouse gases caused by the manufacturing of new textbooks.With GreenTextbooks.org you re not only saving trees, you are saving some green. http://www.GreenTextbooks.org
amazon.co.uk?Ebay?