Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
WishSimply - Wishsimply is a easy-to-use online and mobile service to manage and share your wish lists.
PriceSpy - PriceSpy helps you save money when shopping online.
Dealspotr - Dealspotr is like Wikipedia for deals.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Bustaprice - Price comparison search website for Amazon.com network