If we are talking about this year alone, WW sells, consoles only....
GTA4 (combined two platforms)
Next Guitar Hero or Rock Band game
Couple of caveats. SSBB, I honestly believe is going to be another Metroid Prime, where only the core will care about the game and will never get past 2 mil. Same goes for MGS4. GTA4 is released on two platforms and will end up selling over 5 million WW. WiiFit will be supply constraint just like the Wii. Mario Kart will sell cause its a Mario brand game and a family friendly game that will appeal to Alpha moms better than the wild out of control action SSBB. Rhythm games has the hot hand for the last year and half, and a lot companies will try to capitalize on that. If sells pick up for Rock Band when the sold alone peripherals come out , GH will answer back this year with something big.... Most of the shooters will cancel each other out, not know which will be the big one this year. Don't forget about the X factor Spore that is coming out. If it picks up like the Sims, then it may shatter them all.