As much as Webb seems like a good idea (Secretary of the Navy under Reagan), it won’t be Webb, because the Dems just won his seat in a hard fought battle. They’ll likely lose that seat if he vacates and they need seats in the Senate just as bad as they need the Presidency.
…. BUT, I could see Webb on the Dem ticket in 2012 if things don’t work out this year. And he’ll definitely be on the short list for 2016.