If you buy books--and the odds are if you are reading this you buy too many--you need to stop shopping online at Amazon or Borders or Barnes & Noble.
Why? Because there is a better deal out there.
Check out Abebooks.com. "ABE" stands for Advanced Book Exchange, not an old bald guy in a dusty store. It is a consortium of several thousand online booksellers and several million titles (old and new) in a consolidated marketplace.
The search engine is powerful, and best of all the whole place is market-driven. You will usually find far more copies available in a range of conditions and prices than you do from Amazon, and Abebooks stands behind its transactions.
Often you can even scoop the bookstores; both Pat Buchanan's and Glenn Beck's new books were available here (sometimes in review copies or paperback advance proofs) several days before they went on sale in bookstores, and at cheaper prices.
You do have to watch postage charges carefully, but that's true everywhere.
Try this for reasonable prices on hard-to-find out-of-print titles as well. You won't go back.