App Icon Template - Royalty free app icon creator for iOS, OS X and Android
Sketch to App Store - Generate App Store images for all iPhone sizes from Sketch
Radix Icons - A crisp set of 15×15 icons. Open source.
AppMockUp - Create the most compelling screenshots for your app.
Drawcon - Draw your own app icons
AppLaunchpad - Create free beautiful screenshots for App store/Google play