Wii- 38-40 million
360- 23-25 million
PS3- 20-24 million.
This year will be huge for PS3 and I could severely underestimate the PS3 as PS2 gamers get ready to jump into the next (current) generation by picking up a PS3 as they are familiar with the PS family of systems. (Not all, but a solid majority of those who just have a PS2)
MGS4 will exceed expectations of many here on the forums and sell close to 3-4 million units. The reason I state this is because I never have liked the MGS series and have no interest in the series. But after looking at the Tokyo show demo of the game, it's a MUST buy for me now. All said, it will be a smashing success and huge hit.
There are other games coming out on the PS3 that could impact it, one of which is Socom Confrontation. If they truly make it like a online only HD version of Socom 2 with great gameplay, there will be many old fans of the series who will finally be convinced to take the plunge and pick up the system and game.
I also expect that there will be a surprise hit that will take the gaming industry by storm, and it won't be some casual game that tries to get kids to get "Fit".
I could be overestimating the Wii if demand dies down for the console as there aren't many big games outside of SSBB and MK coming out for the console and the "casual non gamer" lets their system gather dust and not have the desire to pick one up.
My pokemon brings all the nerds to the yard. And they're like, "You wanna trade cards?" Damn right, I wanna trade cards. I'll trade this, but not my charizard.