It looks like Obama might be having trouble in the Midwest, so maybe a fiery midwestern populist/liberal kind of guy. I'm not sure how great of a speaker Sherrod Brown is, but I think he has a lot of appeal up there and could do a good jos hammering Romney on the outsourcing thing.
I'm not sure if Senator Sherrod Brown is going to the DNC this year. He's up for re-election in a swing state this year. And I'm not sure partying it up with the party in Charlotte would help his chances. As preciously stated, Democrats should seal their dominance in the Pacific West and support someone from there, Congressman Martin Heinrich of New Mexico is all but guaranteed that senate seat because of Obama's coattails.