IconGrabber is a tool to extract icons from documents & applications in the form of tiff files. It was developed as a developer tool to get at the 'generic' OSX icons to modify for my own apps, but it'll get the icon as displayed in Finder for anything (except folders.)

To use IconGrabber, just click the 'Grab Icon...' button and choose your victim from the file panel. The file's icon will be saved to your home directory with the name 'iconGrabber' + the date and time, then opened in Preview. It'll be a multi page tiff with each size of the icon on a page - if you only want 1 page, do a save as in Preview.