- Once you've downloaded the app, select Applications in iTunes, right-click the app that you want to extract, and select Show in Finder/Explorer. The file you want is selected automatically when the window opens.
- Copy (that's copy, not move) the file to a different location, for example, your desktop.
- Change the file extension of the copied file from .ipa to .zip using whatever method is most familiar to you.
- Unzip the file using whatever archiving utility you prefer.
- There are a few files, but the directory you are interested in should be named Payload
- This step varies, depending on platform:
- If you are on a PC, simply go into the Payload/
- If you are on a Mac, go into the Payload directory, right-click the file within, and select Show Package Contents.
Props to: Zef and O'Reilly