I didn't reinvent the world here, I just modernized the standard set. The task of creating a whole new representational logic was too great a task for my purposes. Furthermore, the prevalence of these icons makes them easily understood. All icons maintain their original sizes, so they can be used as a drop in replacement.
On OS X, the standard installation location is /usr/share/httpd/icons. This directory is referenced by a global directive in the httpd.conf file. This includes an alias for /icons/ that is resolved for every domain being served. On OS X, this directory is owned by the system (root) with the group ownership belonging to wheel. It is best to follow the same permission model when replacing these files.
Back up the current icons with the following commands:
$ cd /usr/share/httpd
$ mv icons icons.bk
Now download the icon set (here's a preview). Expand the icon set by double-clicking, and then copy to the appropriate location and set thge correct permissions:
$ sudo mv /path/to/downloaded/icons /usr/share/httpd/icons
$ sudo chown -R root:wheel /usr/share/httpd/icons
$ sudo chmod -R 644 /usr/share/httpd/icons
$ sudo chmod 755 /usr/share/httpd/icons
$ sudo chmod 755 /usr/share/httpd/icons/small
The first step simply copies the icons directory to the appropriate location. The second step recursively changes the owner and group for all items in /usr/share/httpd/icons. The next command, sudo chmod -R 644 /usr/share/httpd/icons, changes the permissions to read/write for the owner, and read only for all others, and the -R flag indicates to perform the command recursively. This is the quick way to modify all of the documents. The final commands correct the permissions on the directories, by enabling the execution bit which is required for users to access these directories.
To remove the default header on fancy indexes, place a file named HEADER.html in each directory you want indexed. This should contain html without the closing </body> and </html> markers. If you want this to be global, you can modify your httpd.conf file. Simply search for the line containing HeaderName HEADER.html and set the HEADER.html to /icons/header.html, and place a header.html file in the icons directory.

