clipped from: www.spectator.org   
In order from least plausible to most plausible among the five who fit all the criteria, here's the scouting report:

Mitt Romney:

His resume is a wonder to behold. His competence is readily apparent to any voter.

McCain seems to have developed a personal dislike for him, and McCain is not good at hiding such sentiments.

Minnesota Gov. Tim Pawlenty:

Pawlenty seems able to keep conservatives happy while presenting a friendly persona.

Former House Budget Committee Chairman John Kasich:

There is no doubt that Kasich has an appealing and approachable personality

he can come across as a bit hyperactive, which might exacerbate rather than modulate McCain's intensity.

Rob Portman:

He immediately gives forth an air of (that overused word) gravitas, and he seems to be liked and respected by people across the entire ideological spectrum.

But is he a true Reaganite?

Chris Cox:

The best choice, bar none.

Other columnists have also written that he would make a good Veep choice