http://www.cheapunibooks.co.uk/
Cheapunibooks is a site with only one purpose, to find the cheapest online stockists of university textbooks on the internet. The site is very simple and easy to use, you type in the name and author (or just the ISBN) of the books on your book list, it tells you the cheapest place to buy the books from and how much money you can save off the retail price.
The only problem is it doesn’t seem search for the books very well. I tried it with a few sample book lists on the web and it never seemed to be able to match the books from just the title and the author often only matching one book from 5 or 6 on my list. It often worked better with just the title – though this isn’t very useful as many academic textbooks similar names. If you take the time to make sure it finds all your books it does exactly what is says.
If you do use this for looking for books remember you can often get a better deal at the student union-run second-hand bookshop which many unis have.