December 2009 sales? 2007 and 2008 here for comparison....

[makingmusic476]

Wii - 6.0 million
PS3 - 3.5 million
360 - 2.7 million

Wii will be hard for anyone to predict. It depends heavily on both the reception of New Super Mario Bros. Wii and the possibility of supply constraints  if it does end up being quite popular.