Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Coupofy - Coupofy is USAs number 1 trustworthy deals and coupons website.
Savelist - Found products you want but not ready to buy?
TrackIf - Alerts you if the price of your favorite products drop
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.
Lootr.com - Lootr - Your favorite amazon price tracker. Saving you from paying full price.