Mindzilla :: Icon Grabber
http://www.mindzilla.com/grabber.php

Descarga el favicon de la página que uno especifica

Instructions: Enter a URI and select an image format. The URI can be a domain name or the URI of a specific web page. Press the Grab It! button to get the shortcut icon for that page or site. If the image is displayed in the Grabbed Icon area, save the image. (With our browsers, we can right-click the image and select "Save Picture As..." or "Save Image As...".) If there is a problem grabbing the icon, you will see the "Error!" image in place of the icon. If you have any suggestions, let us know.

http://bitelia.com/2009/03/11/obten-el-favicon-de-cualquier-sitio-en-gif-png-o-jpeg/