This deal has ended.
Amazon, perhaps in response to Buy.com's very public "10% off Amazon" price war, is having an extremely good book promotion: for a limited time, buy 3 paperback books and get the 4th free. Here are the details. Options range from Dr. Suess's Cat in the Hat or Green Eggs & Ham and Harry Potter to thrilers like Angels & Demons and The Broker to classics like The Fountainhead and Catcher in the Rye. Shipping is free if the 4 books total $25 before the discount and there is no sales tax.