I agree that Clark or Richardson would be exciting choices. Other names that I would put in that category would be Michael Bloomberg and Colin Powell, not that I think either will be the choice. Other names that were bandied about but have fallen out of the conversation are Janet Napolitano and Brian Schweitzer. And, of course Clinton is on an entirely different plane than anyone else.
I find neither Bayh nor Kaine exciting, and I don't think they're good choices. Biden may be an acceptable VP choice, but not exciting.
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson