Smartprix - Smartprix is an app by Smartpix.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Price Tracker for Amazon - Price Tracker for Amazon is a shopping app that allows you to browse for favorite products from famous online stores know as Amazon for a better price.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
idealo - Idealo is a free to use mobile application that helps you to find products, compare price and make an informed decision.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.