Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Coupofy - Coupofy is USAs number 1 trustworthy deals and coupons website.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
TrackIf - Alerts you if the price of your favorite products drop
PriceSpy - PriceSpy helps you save money when shopping online.
Lootr.com - Lootr - Your favorite amazon price tracker. Saving you from paying full price.