Steve Kanim, a professor and SPS advisor at New Mexico State, says that you can get UG books about half price from Amazon UK as compared to Amazon US...I don''t know the details but but I know that he has looked into this quite a bit and might have other hints...Gary

NSF Program Director (on assignment from the AIP and the Society of Physics Students to serve as the Robert Noyce Scholarship Program Director at the National Science Foundation)

try icampus.com

Half.com helped me out alot.  It's sometimes a hit or miss as to whether a book is being sold, but you get to pick your price (depending on the book quality.)  It's a subset of eBay.  

I'll have to check out the Amazon UK thing, too!

hey,
you could try looking on ebay.  i've found lots of great and obscure books that way.  most of the time they are old editions, but they work just as well.
happy hunting :)

Buy your used book from www.abebooks.com. Excellent site.

When EBAY does not have it, and you still need it fairly quick-Amazon Marketplace used is the way to go.

The amazon.co.uk trick sometimes works.  I remember seeing somewhere that Hassani's Mathematical Physics was much cheaper in the UK (costing about ~$40 new if I remember correctly), but they must have fixed the loophole, 'cause it's now about the same price as it is on American Amazon.  I just checked Marion and Thornton on both sites and the amazon.co.uk version is about half the amazon.com's price.  I've also heard about slight differences in international versions of texts, though, so you might want to be careful if the books aren't for self-study (although I haven't seen it first hand, so it may just be FUD).

Half.com has a nice assortment.  I bought a few there.  It is a cross between eBay (part of eBay, if memory serves) and Amazon.

Best,

-Art

The best I've found is amazon.co.uk combined with Amazon marketplace.  International editions generally run a lot cheaper than the US version of textbooks.