Store News is a discount discovery app for the iOS and Mac App Stores. It supports smart filters on details of the application or discount, as well as standard filters by device, category, and whether the discounted app is free.
While it's got the basics down, there are a few flaws in existing features that make me pause to recommend this app. The prominently displayed "Store News for iOS" button leads to a dead link; the free/paid filters can stop working unexpectedly; smart filters can't be deleted except with a menu item. One also can't have the application ignore apps one has purchased already without creating a smart filter and adding each app title - a painstaking process that would not be worth the result. It also appears to only provide a list of recently discounted software.
Sam's Protip: Perhaps because of differing criteria for discounts, I've found that each discount discovery app only shows a subset of available discounts. As of this writing, the most up-to-date and comprehensive resource for finding App Store discounts online is the website AppShopper.com.