Trump/Gingrich would be a very entertaining ticket, as would Trump/Christie.
One way to find out if Trump is as incompetent as some say he is, is if he picks Mary Fallin or Jeff Sessions. Fallin has run the state into the ground and Sessions is a total mushmouth.
All that being said, I think Scott Brown is probably the best potential choice among those who would realistically do it.
A thought occured to me the other day. If a majority of the delegates are Cruz delegates, even if pledged to Trump, would they really vote to nominate a pro-choice Vice President?