A word of advice for online shoppers: I had a look at a few books myself, and compared the prices to Amazon. These "discounts" can be very variable. For some books, it looks really like a bargain, while for others, Amazon is cheaper, so I would advise you to check before purchasing. And again, include the shipping costs (which are truly much better on NHBS than Amazon).
And don't forget the publication date, for multiple editions.