There is a website that lets you create price watches on Amazon products. You are alerted to price changes and can browse products with the biggest prices drops. The website is as follows:
Another smart tool is InvisibleHand, a browser extension you can install on Chrome, Firefox, and Safari. Whenever you land on a page selling a product, it automatically searches the web for the lowest prices on the item.
Source: Money Magazine, September 2014, Page 26