The always interesting, often insightful Dick Morris writes in Real Clear Politics that McCain should definitely NOT select Mitt Romney as his vice president nominee. The reasons Morris gives are somewhat persuasive.
Then he makes some suggestions of his own that I think are likewise interesting, but less insightful. He suggests McCain needs to do something major to redefine himself (very possibly true) and to do that suggests Condi Rice, Colin Powell, Joe Lieberman, or Mike Huckabee.
I can see arguments in favor, and against, all four of these. While any except Huckabee would stir up controversy and attention, each has the potential to make the McCain candidacy less attractive to substantial blocs of voters. Perhaps his strategy in selecting a veep should be guided by that old Latin aphorism from medical education: Primum non nocere, that is, First, do no harm.