Not going to be Liebs. As good as his support for the war has been, he would cause the entire conservative part of the republican party to sit it out. They're already dabbling with the notion given their distaste for McCain. Perhaps Liebs could draw an even higher percentage of indy's and crossover dems, but it would be marginal given McCain's natural draw on these groups already. Liebs is a better asset to have in the Senate anyway, where his vote for war and security measures and being a voice of reason among the democrats on and indy's on other issues is very useful.
Unfortunately, I think Romney would make the evangelicals bolt, though I personally like this pick.
Condi... I don't know a damn thing about her politics. I suspect she would say yes if asked, but she has been pretty clear that she is not interested in being asked. From a purely surface level perspective, I think she would be a wash on the ticket. She's highly intelligent, has a top notch resume and probably a strong biographical story, appears to be absolutely tough as nails (no crying on the campaign trail), and she would round out the international diplomatic aspect of a "team ticket". But she doesn't bring anything to the table on non-security domestic politics, which is where McCain needs the most help. She's also stained by the Bush administration and various policies over the last 8 years that aren't popular (McCain has Iraq hanging on his neck, but otherwise is not tied to Bush and is able to distance himself from any number of low popularity policies). And no matter what the republicans do, her choice will be interpreted and spoken of as a cynical attempt to neutralize the race-transcending moment of Obama and the democrat party by nominating him. It will not matter how qualified she is, how likable she is, how serious or obviously good for the position she is... there is only room enough in this race for one transcending candidate and it is going to be Obama. Just ask the democrats how the whole competing transcendent nominees thing is going.
Best to pick a governor with a strong domestic politics background (economics most valuable) who is relatively young, has demonstrated a keen sense of good judgment and ability to live up to a challenging position, and can speak with some inspiration. Probably also best to pick someone who did not run for the nomination.