If you can survive for a few days (read: a week+) without a book and/or borrowing from someone else, you can save a good chunk of change by ordering them from overseas, a la
http://www.amazon.co.uk -- saved me almost $175 on my last semester's worth of books (Spring 04) ... it does take quite a bit of time to get here, though, and you gotta be careful with the currency exchange, since that can bite you (especially since the Euro/GBP seems to be going up against the USD ... but that's another thread).
I've personally never dealt with that website, so I can't compare prices, but I seriously recommend doing anything OTHER than buying them directly from the campus bookstore. Only reason I did that this year is all TA's get a 20% discount on bookstore purchases, which made it cheaper than I could get them online.
YMMV, of course.