I think the consensus is Clinton, Truman, Garfield, George H. W. Bush, and now Obama. (In 1992, with H. Ross Perot, we had three left-handers all contending.) There are arguments for others, but those five seem to stick.
Watch Obama. He uses his hands when he talks, but he leads with his right. This is a man VERY much in command of himself (smoking notwithstanding).