Meebo is another good option, too, particularly if you already have people using it because the IT department has blocked IM software. The one additional feature it has that is worth noting is you can invite people to the room — which you can make public or private — from your buddy lists.

Obviously, Yoni, you’ve keyed in on the primary necessities for this idea to have legs: Whatever is used needs to be Web-based and one-click intuitive. Don’t require anyone to download any software. They may not have the necessary permissions to install it on their machines anyway.