Still something of a long shot for VP, I would suggest that Alaska Governor Sarah Palin would be an interesting choice for McCain because she'd pull some of the soft Obama support from former Clinton folks. Having a woman on his ticket, especially if Obama does *not* have one on his, would help equalize the advantage the democrats currently enjoy for promoting a form of "affirmative action" lacking in American presidential politics for the past 240 years.
Obama's choice? I'd say he's still getting lobbied by Hillary and the gang for her, but that is only about 20% likely. Biden? Maybe, but he's not the military strategist that, say, Wesley Clark or Colin Powell would be which is why I think they are probably on Obama's "A list" for Veeps.