This has been anticipated, but it looks like former Governor Mark Warner is officially unoffocially in the race (official announcement later today) to succeed John Warner as Senator from Virginia. For reasons that are slightly mysterious to me, governor Warner is ridiculously popular in Virginia for someone who was governor for four years a couple of years ago (even my cousin in second grade remembers him fondly), so this has just gone and become a very likely Democratic pickup which, in turn, makes it overwhelmingly likely that Democrats maintain their Senate majority.
UPDATE: Commenters are warning that semi-moderate Rep. Tom Davis would be a formidable opponent, but Rasmussen's polls say otherwise:
In a match-up of former Virginia Governors, a Rasmussen Reports telephone survey finds Warner leading Jim Gilmore by twenty percentage points, 54% to 34%. Warner also starts the season with a comfortable lead over Virginia Congressman Tom Davis. The Rasmussen Reports poll shows Warner attracting 57% of the vote while Davis earns 30%.
I should note that, like Matt Stoller, I'm not really a Mark Warner fan. I am, however, strongly inclined to take what I can get in terms of Democratic pickups in southern states.