Web sites for buying books
www.alldirect.com (this was my favorite, but they went out of business)
www.bestbookdeal.com
www.booksprice.com
www.campusbooks.com
www.bookkoob.com
www.amazon.com (the most famous)
www.A1Books.com
www.aaabooksearch.com
www.isbn.nu
www.bestwebbuys.com
www.bookfinder4u.com
www.bookfinder.com
www.addall.com
www.AnyBook4Less.com
www.firstandsecond.com (Indian; see Rupee-to-dollar currency calculator)
www.Bookpool.com
www.half.com
www.froogle.com
www.campusi.com
www.bigwords.com
www.bamm.com (Boooks-A-Million)
www.barnesandnoble.com
www.alibris.com
www.textbooks.com
www.bestwebbuys.com
www.valorebooks.com
www.bookburro.com
www.virginmega.com
www.abebooks.com
www.elephantbooks.com
www.1bookstreet.com
www.bookwire.com
www.totallycheap.com
www.bookfetch.info
www.bookburro.org (Firefox plugin)
Other lists like this one:
Yahoo list of book price comparison sites
http://www.starburst100.com/top100books.htm
http://rootshell.be/~yong321/computer/buycomputerbook.html
http://www.softpanorama.org/Links/links2bookstores.shtml
The Public Library:
Wake Co., NC public library online catalog