Money Saving Phone Apps

I was introduced to Walmart's Savings Catcher feature on their phone app this weekend and a whole new world has opened up to me. I am curious if any of you have other recommendations similar to this?

FYI: The Savings Catcher feature lets you scan your receipt and Walmart will compare the items purchased against other store's prices. If any of the competitor's price are found to be lower, Walmart will reimburse you the difference in what you paid and the other store's price as store credit.