You're probably sick of my suggestions by now (even though one of them was used and the other is [hopefully] being considered), but it may be beneficial for you to add a usergroup legend. It can easily be done manually (I use the term "manually" lightly; there isn't much work) without use of a plugin.
A usergroup legend is a key similar to a map. On maps, there are symbols, and in a legend, those symbols are explained. The same can be done for the usergroups here.
At the bottom of the site, where the members online list is shown, you can add a color-coded legend of each usergroup.
It would look something like this:
Management -
RG Elite -
Sponsor -
Super Mod -
Moderator -
Registered -
Limited -
Banned
Of course, the order is up to you.