Amazon’s 30 Day Price Guarantee
According to this article at Slate, Amazon.com quietly offers a 30-day price guarantee on any purchase made from Amazon.com. If the price drops on any item within 30 days of your purchase, you can request a refund on the difference by calling the super-secret Amazon Customer Service phone number - 1-800-201-7575, extension 7.
More:
Consumerist
SavvySaver
Tools:
RefundPlease
Amazon Price Watch - will email you price changes on up to 4 items per submission.