I think Nader is insignicant this election. Of course he'll get some votes, but the days of him being a spoiler, I think, are over. Not to say that another spoiler couldn't enter the mix, but not this election, not for the Dems anyway.
Never did like Bob Barr, but I'd guess he'll do better than Nader. If this turns out to be a neck and neck race, maybe Barr would be a spoiler for the Repbulicans by getting even a small margin of votes.
What about Ron Paul?

Is he on the ticket. I laugh, BUT he has a large number supporters. I've seen them pop up during the primary, even on liberal sites. He did very well considering.
TIS