For Obama, I would go with either Joe Biden, or Hillary Clinton. Biden is an experienced, respected member of Congress, who can strengthen the ticket. As for Hillary, Obama might consider her, because, it's conceivable that some of his support might be eroded, by Hillary supporters who stay home, and dont vote, if he doesnt pick her.

I think that Mccain might well go with Romney, to attempt to secure the right leaning Christian voters.

Mitch