The Apple documents on icon sizes is a bit out of date. It does not include the icon for the new retina iPad. And it is not updated for the new 1024×1024 iTunesArtwork requirement.
You need to include a new file that is 144×144 pixels and call it ‘Icon-72@2x.png’.
Then add it to your icons list in the Info.plist file.
Since I have lots of apps, I edited the Info.plist files in BBEdit and cleaned out all of the old icon files. You can also edit them in XCode by right-clicking on the Info.plist and choosing ‘Open As-Source Code’. The original files had the icon information between the ${EXECUTABLE_NAME} and CFBundleIdentifier keys so the new file looks like this.
<string>${EXECUTABLE_NAME}</string>
<key>CFBundleIconFiles</key>
<array>
<string>Icon.png</string>
<string>Icon@2x.png</string>
<string>Icon-72.png</string>
<string>Icon-72@2x.png</string>
<string>Icon-Small-50.png</string>
<string>Icon-Small.png</string>
<string>Icon-Small@2x.png</string>
</array>
<key>CFBundleIdentifier</key>
XCode will use the files to populate the icon display in the summary view, so you can check to see if you did everything correctly. If no icon shows up, make sure they are associated with the app and then drag the icon to the appropriate empty place in the summary. You should get an error message telling you why the icon is not appropriate. Usually it’s a size issue. If it fills in the spot, you probably have a naming issue.
Icon is 57×57 and Icon-Small is 29×29. The rest are obvious from the naming convention. The rest of the sizes are listed in the document, referenced below, along with their intended use.
According to the Apple document Core Foundation Keys you shouldn’t append the .png extension so that the system will automatically use the @2x version when appropriate. However, this doesn’t work for me.
XCode 4.5 doesn’t support any version of iOS before 4.3 so do not use CFBundleIconFile.
You also need to include a file called iTunesArtwork and iTunesArtwork@2x (no .png extension) in your application bundle that are 512×512 and 1024×1024 pixels respectively. Do not list them in the Info.plist file.
Two posts with more info Jared Sinclair and Peter Levine