A 5-step process of elimination
1. Rule out any senators, he will only pick a governor. If you rule out Pres. Bush Sr., we haven't had a non-governor elected for president since Gerald Ford was elected 32 years ago. This year the president will be a senator, so he'll have to have a governor to balance it out.
Therefore, rule out: Paul Ryan, Colin Powell, John Thune, Kay Baily Huchison, Tom Ridge, Frank Keating, and Condi Rice
2. Of the governors we have, both Mitt Romney and Mike Huckabee are more polarizing figures from the primary and because of it, neither would bring a full backing support of Republicans.
Therefore, rule out: Mitt Romney and Mike Huckabee
3. Mississippi Gov. Haley Barbour won't make the cut because of McCain's new campaign criteria requiring no past lobbying work.
So, who do we have left.
Gov. Mark Sanford - South Carolina
Gov. Tim Pawlenty - Minnesota
Gov. Charlie Crist - Florida
Gov. Bobby Jinal - Louisiana
4. McCain has said several times recently that the Republicans have already unified their base, but now need to inspire their base. If you didn't catch it, this was a subliminal foreshadowing of the VP he would pick.
5. There is one of these four Governors that answers several key needs of a McCain VP.
Starting with the most important.
1. Governor (as mentioned earlier)
2. Inspirational (rule out Tim Pawlenty)
3. Clearly conservative (rule out Charlie Crist)
4. Clean record
5. Younger, but with more experience than Obama
This leaves two left and both of these candidates posses all five key needs.
Gov. Mark Sanford - South Carolina
Gov. Bobby Jinal - Louisiana
Who do you think it will be
My pick: Gov. Bobby Jinal - Louisiana