A friend of mine whose daughter graduated from U of Maryland years ago sent her some sites for buying cheaper books, as well as selling them:
" There were some classes where they'd list a book but I'd never actually open it because the tests were based on what you learn in lecture -- so after awhile I wised up and didn't buy the book until I actually needed it for an assignment. I told him don't do that freshman year, but once he gets a feel for how college works. Also, don't buy books from a bookstore, even if they're used -- buy them directly from other students or buy them used from a site like bookholders.com, half.com, ebay, amazon, campusbooks.com, etc. (Shop around using a site like addall.com)"