What about McDonnell?
As for Portman, I think he'd make a great runningmate but doubt he'd be willing to abandon his Senate seat so quickly. Besides, I think the GOP would benefit more by keeping Portman in that seat than as VP.
LOL, reason why people run for Senate in the first place is that they daydream about being President or VP, so I really doubt Portman (or anyone else, for that matter) would really turn it down if offered.
Why do we never hear about Richard Burr in veepstakes, he seems to compliment Romney well: Senator, Southerner, Protestant (evangelical?), from a swing state, reliable voting record.