Here is an interesting site that compares the prices of books offered by over 40 + book seller sites. Useful for finding the right book at the right price.
http://www.addall.com/ Addall.com book price comparison It appears to be an easy way to start your search. It is international and has a currency converter built in so it will work for our members world wide which is nice.
It also has sites for magazines, DVD's and music CD's so that's a bonus for some.