Cydia - An alternative app store for jailbroken devices.
Apple App Store - Install apps on your iDevice via the App Store.
Fnd - Browse Apple App Store and iTunes on the Web
AppRecs - AppRecs sorts through reviews in the App Store and automatically helps you filter out inauthentic results.
iNoJB - iNoJB, formerly iNoCydia, is an amazing Cydia alternative requiring no jailbreak!
TheAppStore.org - Find apps by rating, price, category, updated date and more