PriceLocal - Find local stores that match Amazon's price
RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
Rocket Money - Find your paid subscriptions and cancel with one click
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
Bobby - Keep track of your subscriptions
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.