I say Mir vs. Big Nog. The only thing Mir is really good at is BJJ, and Nog is better at it. Plus, Nog has pretty good standup.
Cote is also a pretty big underdog. He has said that he's going to walk forward and rely on his power and his chin. Leben did the same thing...
I don't think Fitch is that big of an underdog. He will go to, and lose, a decision IMO.
Florian vs. Huerta could also go either way. I don't see why everyone is all over Florian's nuts all of the sudden. He's a good fighter. They both are. But neither of them are elite fighters and either one can finish it.
Rashad is a decent underdog IMO, but he has a tendency to hold out for a boring decision when I least expect it. I thought Tito was going to smash him, and pretty much did, but he got a draw. He could go the distance, but I sure as hell hope not.