Makeappicon.com helps designers, developers and project managers make and resize icons for iOS and Android apps. It is an icon resizer which optimizes your app icon designs automatically, and generates icons of all sizes you need before you submit your applications to app stores.
It even outputs a valid AppIcon image set; just drop the directory into your Images.xcassets folder, and you're good to go! Learn how to import into XCode.
About the creator
Check out http://filetypeicons.com/ for free-to-use app icon templates made by us!