One is Larry Summers who served as Treasury Secretary for President Clinton before becoming president of Harvard.
Also Tim Geithner, who has been central during this financial crisis. He's the president of the Federal Reserve Bank of New York. He's been talked about as a leading candidate.
One candidate who is more of a long shot is the former Federal Reserve Chairman Paul Volcker, who is a close adviser to Obama. He's likely to continue to be a top adviser but the two top candidates right now are Geithner and Summers.