Sell them on half.com
I bought my books the first 3 semesters, then I just stopped because I spent $100 on a phyco book I never used, and $90 on a book that was about four levels over the class's head, thus we never sused it.
This year my "math" book cost $160, paperback, the school store bought them back in perfect shape for $20. I didn't buy the book. Also didn't buy my History books, I just checked out some of them from the library.