Since there's a PS3 thread for their games, 360 and Wii should get equal time. I'm sure someone else will start the Wii thread soon enough.
For me, Xbox 360 games I'm looking forward to (with release dates as of this writing):
GTA4 (NOW!)

Supreme Commander (5/12/08)
Ninja Gaiden 2 (6/3/08)
Alone in the Dark (6/24/08)
Guitar Hero: Aerosmith (6/28/08)
Sid Meier's Civilization Evolution (7/9/08)
Soul Calibur 4 (7/29/08)
Too Human (8/12/08)
Mercenaries 2 (8/31/08)
Star Wars: The Force Unleashed (9/16/08)
Fable 2 (10/01/08)
Fallout 3 (10/07/08)
Prototype (10/21/08)
Dead Space (10/28/08)
Halo Wars (11/01/08?)
Gears of War 2 (11/03/08)
Tomb Raider: Underworld (11/03/08)
Mortal Kombat vs DC Universe (Fall '08)
All Points Bulletin (TBD)
Guitar Hero 4 (TBD)
Street Fighter 4 (TBD)
In 2009:
Resident Evil 5
Borderlands
Alpha Protocol (2/2009)
Bioshock 2 (Oct/Nov 2009)
Alan Wake
And I'm sure there's others I've missed. Damn...I'll go broke buying all those games!
