Good point on the groups. It might be a good idea to make a "Groups Recruiting" notecard available to hand out in the welcome area, or at newcomer events. This could explain what the various established groups are involved in and could point folks to a friendly group representative.
It would also be nice to collect a sort of "history" on some of these groups. Where they came from, what their lineage is, etc.
Groups on the main fall into the following categories:
Theme communities.
Specific activities or projects.
Neighborhood associations.
People who are friends or business partners, and want to say so.
and lots are simply people who want to spread around a goofy or clever title.
Anyway, I'm a rep for the Kazenojin. We are a theme community dedicated to the art of flight, both by building great flying craft and by scripting movement. Many of our members are notorious scripters here in SL, and we also have some very good builders. We also are known for a tendency to make things explode.

Our most significant accomplishment to date has been the Air Station. It is torn down now, but for a long time it was the single most impressive and gargantuan build in the world. Progress is under way on a smaller more refined version of the air docks.
I could name a few names who might possibly be good contacts for a few of the other theme communities.
Alek Wu and Merriman Brightwillow: Darkwood, the medieval theme community.
ramon Kothari, CrowCatcher Valen, or Garth Fairlight: Americana.
Gwydeon Nomad: SLittle Tokyo - the theme community dedicated to anime and Japanese culture.