No VP is going to get Romney the presidency. The best thing a Veep candidate can do is not lose you the election. No Veep has ever won an election for their candidate - but some have lost, or nearly lost, the election for their candidate (Palin in 2008, Quayle in 1988). Romney is going to have to win this on his own, not based on a great Veep pick. If the Veep were so great, he'd be the candidate, not Romney.
Ron Paul's politics are so diametrically opposed to Romney's that they would be a train wreck of a ticket. Every time Paul opened his mouth he'd contradict his candidate, something you really don't want on the ticket.
I'd expect Marco Rubio to get the call. He could help Romney swing Florida, which Obama took in 08.