Bill Frist, Republican Majority Leader in the Senate, Jeb Bush; Florida Governor, Rudy Guillani Former Mayor of New York City, George Pataki. Governor of New York. Newt Gingrich, Former Republican Speaker of the House. (can only see him in a VP slot).
John McCain, Senator from Arizona. John Ashcroft; Attorney General of the United States, Elizabeth Dole, Senator North Carolina, wife of Bob Dole. She was also the past president of the American Red Cross for a number of years before leaving that to run for the senate. Hayley Barbor, Gov of Mississippi and former Chairman for the GOP.
I don't believe Colin Powell is even a potential in this list. He's ready to retire. Nor do I think Don Rumsfield either. He's 71-72 now.
Bill Richardson, Gov of New Mexico and former UN ambassador under President Clinton,Hillary Clinton, Senator from NY. Charles Shumer; Senator from NY. Nancy Pelosi, Present House Minority leader. John Kerry (if not in 04) and Al Gore.
Topics of Interest; Missile defense, (US Missile Defense in Alaska comes online before end of year),Nuclear Proliferation, Nuclear Armed Iran, Homeland Security, Taiwan/China. Greater EU expansion/ EU economy/ EU Military and possible realignment of NATO in next 4 years.
That's all I can think of off the top at the moment.