iOS (iPhone/iPad) icon sizes and names explained

So each device type/size combination should have 2 icons:
the Application icon
the Spotlight/Settings icon


Additionally you should have an iTunesArtwork File but its not required.  Technically the only "required" icon is the Application icon.

Original iPhone/3/3s/iPod Touch icon sizes and names:
Icon.png (57x57)
Icon-Small.png (29x29)

For Retina icons for the iPhones & iPods we double the resolution in both directions and add "@2x" to the name
Icon@2x.png(114x114)
Icon-Small@2x.png (58x58)

For the iPad 1 & 2 we need the same icons but they have different naming requirements
Icon-72.png (72x72)
Icon-Small-50.png (50x50)

And again, for the new retina iPad we need to make "@2x" versions so
Icon-72@2x.png (144x144)
Icon-Small-50@2x.png (100x100)


So, for a complete universal app that supports all screen sizes you want to create:
Icon-Small.png (29x29)
Icon-Small-50.png (50x50)
Icon.png (57x57)
Icon-Small@2x.png (58x58)
Icon-72.png (72x72)
Icon-Small-50@2x.png (100x100)
Icon@2x.png (114x114)
Icon-72@2x.png (144x144)


Additionally you'll probably want to make the iTunes Artwork icons
iTunesArtwork.png (512x512)
iTunesArtwork@2x.png (1024x1024)