Think about who wins presidential elections. G.W. Bush, Clinton, Reagan, FDR all govenors or ex-governors. Other than Clinton a govenor of a fairly good sized state. Now a VP like G.H.W. Bush on rare occasions win and VPs, like LBJ and HST can succeed a president that dies and win reelection. But Senator are very rare, with JFK being the only sitting Senator in many years to win. Chenney could win, but he says he is not running now.
So with Arnold out due to not being native born, to me that makes the list:
1. Jeb Bush
2. Mitt Rommey
3. George Pataki
4. Rick Perry
5. Matt Blunt
6. Bill Owens
7. etc.
Now Frist quiting the Senate and running as a private citizen ala Carter in 1980 is an interesting twist, maybe that is what it takes for a Senator to win the presidency? Rudy has run a city the size of many states so maybe he belongs on the list. I see no way an old McCain still in the Senate has any shot.
George Allen a Senator who was a governor is an interesting case. Do we elect ex-governors for their administrative experience or do we not elect Senators because they have such a long record of votes and so many compromises that their opponents can use against them.
Neophytes like Rice just have no electoral experince and if you are not Ike a huge war hero, I doubt you can win the nomination or the general. It would be interesting to run a Tommy Franks or Swartzkoff. It stir the DU crowd up, of course it is not like they need much stirring.
That is about the list to me. I would be discussion govenors and let the press talk about Senators and be wrong as usual, if I were you.
Rick Perry will be hard-pressed to win renomination or reelection in 2006; I don't think even he is thinking of early presidential primaries.
Allen is a past governor.
You forgot Pawlenty.