App Store Inspiration - Best iOS App icons, screenshots, landing pages & heatmaps
App Icon Template - Royalty free app icon creator for iOS, OS X and Android
Radix Icons - A crisp set of 15×15 icons. Open source.
MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
Drawcon - Draw your own app icons
App Icon Resizer - A service to resize your app icon to all needed resolutions