A jabber chat client that displays a list of rooms?
So the answer to my question is to use Adium. A lucky discovery: I was about to disconnect my chat account using the File menu, but when I moused over the text "Disconnect: ...", a context menu appeared as one might expect. However, I had never clicked the item labeled Discovery Browser. Under the server's "Public Chatrooms" I found a list with the JID of all the active chat rooms.