Tom Brokaw has recently been suggesting Al Gore as VP and energy Czar - to both Gore and Obama. That is an interesting prospect, and, for me, I couldn't think of a more persuavive, and credible, addition to his pitch.
Value wise I'm definitely more in line with Obama, but there is nothing worse than the inability to deliver on such promises, most likely creating the reverse. McCain is a military guy, and although a good one, the upper ranks of the DC military establishment definitely need a wipping. Bringing him in to cover up the mess could also lead to as negative a result as a failed Obama presidency.
Joseph Lieberman has been talked about as a Lieutenant for McCain. This is interesting, but I don't think realistic. More likely McCain will promote a younger member from his own party. I'm not capable of guessing who might be on the short list, but if he can select a member of the GOP that can credibly continue McCain's legacy than that too would be a very powerful team.
If McCain can find a Republican woman in her 40's or early 50's who is also a credible maverick and a 'compassionate conservative' that individual would likely be the first female president of the US... regardless of McCain's success or failure.