It will not be Wii Fit, alas.
SSBB, Spore, MGS4 all stand a chance, as does whatever Nintendo unveils for this year
GTAIV stands a small chance, but I don't think it can win, being in the same year as MGSIV
Similarly, SSBB will ruin Mario Kart's chances
I doubt Starcraft II will get it.
LBP planet is awesome, but not GOTY material