OctoShop for Chrome - Compare prices and get alerts when things are back in-stock
RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
Avast SafePrice - Avast SafePrice is one of the leading online services that provide buyers with information about the latest price comparison of the products, deals, and discounts, and coupons.
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.
Wikibuy - Find lower prices at other sellers while you shop on Amazon
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything