Here are a few site where I get my books from other then B&N or Amazon (If you have any other sites that you enjoy please feel free to share them with me, I love saving money on books):
*Paperbackswap (not really a book store but it's a great place to save money on books!)
*Betterworldbooks: This site is awesome because you get free shipping on all your books and you don't have to spend any specific amount! I love it. http://www.betterworldbooks.com/
* http://fictiondb.com/ : this is a cool little site that will make book suggestions for you by comparing books that you like to read.
*Netgalley is a great and free site, allows readers to get their hands on ARCs. There are a great deal of publishers that use this site.