As requested....
Search and Compare among 40+ sites, 20,000 sellers, millions of books!
I learned of AddAll.com while I was in college and I credit this site with singlehandedly saving me hundreds of dollars (unfortunately I didn't learn about it in my early years of college or it could have been a thousand or more). This site does what it says, but has now expanded to include music, movies, magazines, and most recently credit card offers. While I have not used it for anything other than books, I can attest to the value of the searches. It conveniently allows you to search for books by keyword, title, author, and (most valuable to students) ISBN.
Very Good (Printed) Book Search SiteA suggestion on usage for the students out there...Go to the bookstore when the book list is first published. Get the ISBN numbers off the listings, then search here. I found on average I was paying about 30% of my school bookstore prices if I could get them used, and about 60% new. Doing it this way guarantees you get the exact same edition. The only books I ever bought at the school bookstore were school publications (often handbooks that the teachers put together and published locally only).
Very Good (Printed) Book Search SiteBest of all, AddAll will determine the prices for you AFTER calculating shipping. Very handy for those sites that lure you in with low cost goods, but are actually more expensive because they charge high shipping rates. Lastly, you can link to the site to buy the book. Here is an example of the results:
Very Good (Printed) Book Search SiteAll in all, a VERY useful site.
all pictures from http://www.addall.com