Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.

RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.

Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.

Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything

Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.

Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.