Right now all the scuttlebutt out there is seemingly pointing to a McCain-Romney ticket. I can definitely see both the advantages and disadvantages of that option.
Romney's younger, he's dynamic, he's an economic powerhouse (in the sense that he's a very successful CEO), he's got an entire voting bloc by the proverbial short hairs in that I think a good majority of them feel that he is the fulfillment of the White Horse Prophecy. I mean, he got 90+% of the Utah vote. I think he's probably going to do that nationwide with Mormons.
Romney's a Mormon (doesn't play well in the Bible Belt), he's done some flipping and flopping, and Taxachusetts doesn't seem like they like his Universal Health Care that much.
At the same time, from a voting bloc perspective, I don't know that he's a negative. Sure, McCain will lose votes in the South, but the only state where that matters is Virginia. It doesn't matter in Florida, but the other states are solid enough that McCain could get defections and be okay. At the same time, Romney helps him a lot in Michigan, Colorado, Nevada, Massachusetts, and perhaps California. That doesn't mean that he'll deliver all those states, but he'll certainly make McCain far more competitive there, to the point where the electoral math could very well fall McCain's way. I'd consider Romney the safe choice, even though choosing a Mormon doesn't seem like that would be the case.
What I would like to see however is something that is far more risky, but could blow the thing wide open. McCain would either win by a landslide or lose by a landslide. That pick is Joe Lieberman, former Democratic Veep choice and current Independent Connecticut Senator. I know that this would cause a lot of conservatives to throw a conniption fit, but think about it for a minute. Most of the nation defines itself in the middle of the political spectrum. Sure, they're not "the base" or even terribly active in politics. You don't have any blowhards out there on radio or TV spreading the moderate gospel, but those voices are there. They got John McCain elected as the Republican candidate and they are a force to be reckoned with. They're the people who were initially enticed by Obama's message of change. What better weapon could McCain pull out of his arsenal other than some actual change - for the first time in the history of the Republic, a major party ticket would have moderates from each party on the ticket. Lieberman brings some demographic advantages (he sews up Florida and could perhaps make New England/New York/New Jersey/Pennsylvania competitive or even Red) that I think outweigh his negatives (low GOP turnout in their current strongholds). Let's face it, the Republican base isn't satisfied with McCain as their standard bearer to begin with. Putting Romney or Ron Paul on the ticket won't change that. Their beef is with McCain the moderate - as though being moderate is somehow a completely unacceptable option. Let me tell you, I'm sick of Republicans who want to throw everyone out of the party who doesn't fit their definition of the party. Let anyone who wants to be a Republican be a Republican. If you don't agree with their politics, vote for someone who you do agree with. Don't throw your vote to the other side of the aisle in hopes that the other guy will get elected, thus making conditions perfect for you to say "I told you so" to everyone else. Anyway, end rant.
Lieberman would be amazing, and even though I don't agree with his politics on a lot of issues, I know that he and McCain are very good friends and would work together well even though they are in different parties. This more than just about anything else I can think of would have the potential to energize people about the political process again and perhaps turn things around to the point where you'd get more involvement and turn the tide. In the process, I think it'd get McCain elected. Of course, he might not be, but it would shake things up and that's what I think we need a little more of.