I think Jim Webb's the most likely pick - he helps Obama play geographic offense (Virginia, along with Colorado, is his chief red-state pickup target especially with Mark Warner running a strong and very well-financed campaign there), he's the classic macho white guy who matches McCain's Naval Academy and Vietnam vet bio, he provides a cost-free patina of bipartisanship without actually disagreeing with the party line on any issue of consequence...the downside is that he's also a very inexperienced and, to put it mildly, unpredictable campaigner and debater. I could easily see Webb play the "I served and you didn't" card in a debate while completely forgetting who the top guys on the ticket are.

Among the women, I would think Kathleen Sebelius, since she's a heartland-state governor and is, shall we say, not as un-telegenic as Janet Napolitano. Like McCain, Obama would be fool to take another Senator with no executive experience (at least Webb has been a Cabinet Secretary).

Obama will also be tempted to take a man-in-uniform type like General Anthony Zinni or Wes Clark, but Webb is green enough as a politician; taking a complete political novice and domestic-policy cipher may not be as disastrous as it would be for McCain, but it's still a high-risk strategy. It didn't work out well for Ross Perot, and you can't pick a more distinguished miliary man than Jim Stockdale. Also, Wesley Clark is nuts, and looks nuts (the man never blinks).

Then there's the Rust Belt governors, Rendell and Strickland. Assuming they hold up under vetting, which may be a questionable assumption in both cases, I could see the case for them, but Strickland's basically a nonentity who backed into the governorship and Rendell is just more big-city machine-politician than a guy from Chicago needs. Rendell's great on TV, though.

But I would not count out Bill Richardson - yes, it would mean two non-white males running together, but Richardson covers all the kinds of experience you could want, he's an excellent retail campaigner (though a poor, gaffe-prone debater), would excite Latinos and help put more Western states in play. If I was advising Obama, I might lean towards Richardson.

Adam C: If I were advising Obama, I'd recommend a shortlist of Strickland, Rendell, Sebelius, Webb, and Richardson in that order. The GOV of large swing states where Obama polls below the generic D are at the top of the list for electoral purposes.

The only major problem with them (barring a vetting issue) is that neither has foreign policy experience. I'm not sure how big of a deal that will be to Obama's decision-making.

Sebelius and Webb both will probably appeal to Obama's "change" mentality as they are not run-of-the-mill Ds.

Dark horses i