Ben Waldie, who is, in my opinion, probably the most savvy AppleScript author not actually working for Apple recently published a script on TUAW that automatically extracts an icon from an application. I created a similar service using scripts I learned from Sal Saghoian's AppleScript 1-2-3 book a few years ago but Ben's solution is much better. I've added it to my script menu and if you ever have need of app icons, you should too.

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