Cydia - An alternative app store for jailbroken devices.
iNoJB - iNoJB, formerly iNoCydia, is an amazing Cydia alternative requiring no jailbreak!
Apple App Store - Install apps on your iDevice via the App Store.
Hydia - Hydia is a non-jailbroken version of cydia wich allows you to customize your device in many ways.
Sileo - An APT package manager for jailbroken iDevices.
Altstore - A home for apps that push the boundaries on iOS