Brian Schweitzer with a progressive woman or African-American or Latino running mate. I think Schweitzer would carry all of Obama's 2012 states and North Carolina. He'd also put the Republicans on the defensive with white rural voters. I don't think Schweitzer would win a majority of these voters, but he'd make leaps and bounds of improvements over Obama. I also think he'd have a coattail effect in House races.
Ah, I forgot about Schweitzer! Along with Brown and Warren, my favorite Democrats. I'd love to see Schweitzer run.