Buying books online is cheaper, to be sure, but nothing beats walking into a Borders or Barnes & Noble, and being completely surrounded by thousands of books. It is nearly impossible for me to walk in to either one of those stores and not walk out with something.
The Barnes & Noble near me as an excellent bargain section. I just recently purchased the hardcover editions of THE GIVEN DAY by Dennis Lehane and CHILD 44 by Tom Rob Smith for $4.99 and $5.98, respectively.