GOP:
Bill Frist
Bill Owens
Rudy Guiliani
John McCain
Tommy Franks
Rick Santorum
Mitt Romney
Colin Powell
Frist- He's running.  He's a saint, traveling to Africa every year to give free medical care.  Southern.  But I don't get the vibe.
Owens- Beloved in Colorado, but he has an odd look, and I think he's short.  I don't get the vibe.
Rudy G- Hero of 9/11, tough on crime, proven commodity.  Liberal on social issues...too liberal?  I get the vibe.
John McCain- Wolf in sheeps clothing.  people think he's moderate, when hes very conservative. War hero.  Western.  Definitly get the vibe.
Tommy Franks- The brains behind the stunning success of the Iraq War (the initial part of it).  Very well educated, recognized, and well spoken.  Comes from Texas.  Big time vibe.
Rick Santorum- Social and fiscal conservative from Pennsylvania.  Young, and opinionated...maybe too opinionated.  May have problems carrying his own state in the general.  Don't get the vibe.
Mitt Romney- Massachusetts Republican.  Mormon.  I don't think the country is ready for a Mormon President.  Don't get the vibe.
Colin Powell- The dark horse.  Always denies running.  Might decide after another 4 years that to fix problems in government he might have to do it himself.  Slight vibe.
Prediction: McCain/Giuliani
Dark Horse Prediction: Franks/Santorum
Edit:
I forgot Chuck Hagle, the Senator from Nebraska.  He's a moderate conservative, from a midwest state.  Tough talker, war hero.  No vibe for President, but could easily see him on the bottom end of both a Franks and McCain ticket.