Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
PriceSpy - PriceSpy helps you save money when shopping online.
Savelist - Found products you want but not ready to buy?
Shopping.com - Shopping.com is a leading price comparison site that allows you shop online for the best deals and lowest prices. You can read unbiased product reviews and compare prices online. Online shopping has never been as easy!
PriceGrabber - Get the lowest prices on computers, electronics, furniture, cameras, clothes and more.