These are all the games that are absolutely confirmed with announced publishers, they're not tech demos or shown teasers with no offically announced names. It 's hard to go through the crap that IGN has..
edit: edited after the xbox japanese summit.
Gears of War (Microsoft Game Studios)
Kameo: Elements of Power (Microsoft Game Studios)
Perfect Dark Zero (Microsoft Game Studios)
Project Gotham Racing 3 (Microsoft Game Studios)
Too Human (Microsoft Game Studios)
Everyparty(Microsoft Game Studios Japan)
Ninety-Nine Nights (Microsoft Game Studios Japan)
Blue Dragon (Microsoft Game Studios Japan)
Lost Odyssey (Microsoft Game Studios Japan)
Need for Speed: Most Wanted (Electronic Arts)
The Godfather: The Game (Electronic Arts)
Madden NFL '06 (Electronic Arts)
FIFA '06 (Electronic Arts)
NHL '06 (Electronic Arts)
NBA Live '06 (Electronic Arts)
Tiger Wood PGA TOUR '06 (Electronic Arts)
Battlefield 2: Modern Combat (Electronic Arts)
NBA 2K6 (2K Games)
NHL 2K6 (2K Games)
Amped 3 (2K Games)
College Hoops 2K6 (2K Games)
Top Spin 2 (2K Games)
Elder Scrolls IV: Obliviion (2K Games)
Prey (2K Games)
Peter Jackson's King Kong (Ubisoft)
Tom Clancy's Ghost Recon 3 (Ubisoft)
Killing Day (Ubisoft)
Call of Duty 2 (Activision)
Tony Hawk's American Wasteland (Activision)
Quake 4 (Activision)
GUN (Activision)
Condemned: Criminal Origins (SEGA)
Full Auto (SEGA)
Chrome Hounds(SEGA)
Frame City Killer (Namco)
Ridge Racer 6 (Namco)
LOVE FOOTBAL (Namco)
Rumble Roses Double XX (Konami)
Pro Yakyu Spirits (Konami)
Winning Eleven 10 (Konami)
Dead Or Alive 4 (Tecmo)
Dead Or Alive: Code Chronus (Tecmo)
Dead Or Alive Extreme Volleyball 2 (Tecmo)
Saint's Row (THQ)
The Outfit(THQ)
Dead Rising (Capcom)
Resident Evil 5 (Capcom)
The Darkness (Majesco)
Demonik (Majesco)
Huxley (Webzen)
APB (Webzen)
ZooKeeper (Success)
Operation Darkness (Success)
Stranglehold (Midway Games)
Test Drive Unlimited (Atari)
Tomb Raider: Legend (Eidos)
eNCHANT arM (From Software)
Final Fantasy XI (Square Enix)
KOF Maximum Impact 2 (SNK)
Dynasty Warriors 5 SPECIAL (Koei)
Mobile Suit Gundam (Bandai)
Super Robot Taisen (Banpresto)
Wrestle Kingdom (Yukes)
Zoids (Tomy)
Tokyo Extreme Racer (Genki)
T4: Tetris the Grand Master (Arika)
World Airforce (Taito)
Total: 67 titles.
Feel free to make corrections/addition. NO BS titles with no publisher or official title announced.
Addendum: possibly soon to be added to the list:
Alan Wake
Forza Motorsports 2
Halo 3
Marvel MMOG
Shadowrun FPS
Unannounced Game Republic Title 2
Unannounced Miziguchi Title 2
Unannounced Real Time Worlds Title
Unannounced Namco RPG
Unannounced Bandai Exclusive
Unannounced Konami Titlte
Project Progressive (Tecmo)
edit: edited after the xbox japanese summit.
Gears of War (Microsoft Game Studios)
Kameo: Elements of Power (Microsoft Game Studios)
Perfect Dark Zero (Microsoft Game Studios)
Project Gotham Racing 3 (Microsoft Game Studios)
Too Human (Microsoft Game Studios)
Everyparty(Microsoft Game Studios Japan)
Ninety-Nine Nights (Microsoft Game Studios Japan)
Blue Dragon (Microsoft Game Studios Japan)
Lost Odyssey (Microsoft Game Studios Japan)
Need for Speed: Most Wanted (Electronic Arts)
The Godfather: The Game (Electronic Arts)
Madden NFL '06 (Electronic Arts)
FIFA '06 (Electronic Arts)
NHL '06 (Electronic Arts)
NBA Live '06 (Electronic Arts)
Tiger Wood PGA TOUR '06 (Electronic Arts)
Battlefield 2: Modern Combat (Electronic Arts)
NBA 2K6 (2K Games)
NHL 2K6 (2K Games)
Amped 3 (2K Games)
College Hoops 2K6 (2K Games)
Top Spin 2 (2K Games)
Elder Scrolls IV: Obliviion (2K Games)
Prey (2K Games)
Peter Jackson's King Kong (Ubisoft)
Tom Clancy's Ghost Recon 3 (Ubisoft)
Killing Day (Ubisoft)
Call of Duty 2 (Activision)
Tony Hawk's American Wasteland (Activision)
Quake 4 (Activision)
GUN (Activision)
Condemned: Criminal Origins (SEGA)
Full Auto (SEGA)
Chrome Hounds(SEGA)
Frame City Killer (Namco)
Ridge Racer 6 (Namco)
LOVE FOOTBAL (Namco)
Rumble Roses Double XX (Konami)
Pro Yakyu Spirits (Konami)
Winning Eleven 10 (Konami)
Dead Or Alive 4 (Tecmo)
Dead Or Alive: Code Chronus (Tecmo)
Dead Or Alive Extreme Volleyball 2 (Tecmo)
Saint's Row (THQ)
The Outfit(THQ)
Dead Rising (Capcom)
Resident Evil 5 (Capcom)
The Darkness (Majesco)
Demonik (Majesco)
Huxley (Webzen)
APB (Webzen)
ZooKeeper (Success)
Operation Darkness (Success)
Stranglehold (Midway Games)
Test Drive Unlimited (Atari)
Tomb Raider: Legend (Eidos)
eNCHANT arM (From Software)
Final Fantasy XI (Square Enix)
KOF Maximum Impact 2 (SNK)
Dynasty Warriors 5 SPECIAL (Koei)
Mobile Suit Gundam (Bandai)
Super Robot Taisen (Banpresto)
Wrestle Kingdom (Yukes)
Zoids (Tomy)
Tokyo Extreme Racer (Genki)
T4: Tetris the Grand Master (Arika)
World Airforce (Taito)
Total: 67 titles.
Feel free to make corrections/addition. NO BS titles with no publisher or official title announced.
Addendum: possibly soon to be added to the list:
Alan Wake
Forza Motorsports 2
Halo 3
Marvel MMOG
Shadowrun FPS
Unannounced Game Republic Title 2
Unannounced Miziguchi Title 2
Unannounced Real Time Worlds Title
Unannounced Namco RPG
Unannounced Bandai Exclusive
Unannounced Konami Titlte
Project Progressive (Tecmo)