Get iOS iTunes App Store ID of an app itself?

You way use iTunes Search API to look up your and other apps on the App Store.

Docs: http://www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html

Example: http://itunes.apple.com/search?media=software&country=us&term=raining%20weather

iTunes may return more then one result, but you can filter results by bundleId. trackViewUrl will contain iTunes URL to your app. trackId will contain app's ID.

Here is the answer.

1. The app requests http://itunes.apple.com/lookup?bundleId=com.clickgamer.AngryBirds
2. Find the "version": "2.1.0" and "trackId": 343200656 in the JSON response.

Warning: This API is undocumented, Apple could change it without notice.

References:

[1] https://github.com/nicklockwood/iVersion/blob/master/iVersion/iVersion.m#L705
[2] https://stackoverflow.com/a/8841636/41948
[3] http://ax.phobos.apple.com.edgesuite.net/WebObjects/MZStoreServices.woa/wa/wsLookup?id=343200656&mt=8
[4] http://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/wsSearch?term=+Angry+Birds&country=US&media=software&entity=softwareDeveloper&limit=6&genreId=&version=2&output=json&callback=jsonp1343116626493