I recently wrote a simple plugin that modifies the look of ActiveStates Komodo IDE/Editor on Linux. I used stock GTK icons to accomodate for as many icons as I could, mainly the directories which looked out of place in gnome. I used the GTK stock icons as a reference.
Mozilla Firefox 3 uses moz-icon://gtk-directory to display the gtk stock icons for directories, so that means Komodo is able to use the same feature. You can see a thread discussing this here.
GTKLook Plugin: Download