I just finished my first pass of my mimetype -> icon website : http://www.stdicon.com/.
If someone gives me the file extension ".doc" then that maps to the mimetype "application/msword" which, if I don't have an icon for, should show an icon for "application/vnd.oasis.opendocument.text" (or visa-versa).
Is there any clustering of mimetypes, or a hierarchy to search for the correct icon? I'm sure desktops have to solve this problem, how does gnome or kde do it?