Most of the names I've heard mentioned for McCain's choice of VP are "do no harm" choices. They aren't likely to get anybody real excited, but they wont cause a lot of controversy. Rice would be an exception, but he's not going to call on her because she's too close to Bush and doesn't want the job.
One that hasn't been talked about much, but that I believe would be a home-run, would be Steve Forbes. Some points to ponder:
Conservatives and Capitalists would be ecstatic. They've been reluctant to jump on the McCain bandwagon up to this point. With Forbes on the ticket, all that goes away. While the left would paint him as the ultimate corporate insider, I think most Americans concerned about the economy would be receptive of a very successful CEO.
He's been thouroughly vetted. He's run for president himself, has his own magazine and is a regular on TV once a week. Nothing about Forbes' positions is going to surprise or shock anyone. He can certainly hold his own in a debate and he's been speaking in public since he was able to talk.
As far as special interest influence, he's untouchable. He has more money than God. What are you going to bribe him with? Knicks tickets? I don't think so.
He compliments McCain well. Both have the "maverick" image going for them. Together they would present a ticket interested in actually solving problems and getting things done as opposed to "winning the news cycle"
I don't expect it to happen. I'm sure McCain's advisers are looking for a fresh face or a swing state pick. Sure would be nice if competence counted for something, but in politics, it rarely does.