Activision
AQ Interactive
AGFRAG
Artdink
Atari
Atlus
BANPRESTO
Barking Lizards
Blitz Games
Buena Vista Games
Capcom
Cellien Studios
Coresoft
Crossbeam Studios**
D3Publisher
Day 1
Eidos
Electronic Arts
Emerging Entertainment
EPOCH
From Yellow to Orange**
From Software
Gearbox Software
Genki
Grand Prix Games
Grasshopper
High Voltage
Hudson
Ignition Entertainment
Interactive Brains
IR Gurus
JALECO
Koei
Konami, Kojima Studios
Krome Studios
Lucasarts
Majesco
Marvelous Interactive / Natsume
Mastiff
Midway Games
Milestone
MTO
Namco Bandai
Nippon Ichi
Neko Entertainment
NIBRIS
oeFun, Inc
Papaya Studios
Red Tribe
Route24**
SEGA
Sensory Sweep
SNK
Spike
Square Enix
Success
Taito
Take-Two
Tecmo
Terminal Reality
The Game Factor
THQ
TOMY
Totally Games
Tuna Technologies
Ubisoft
Vivendi Universal Games, Sierra Online
Warner Bros. Interactive

Please tell me if I am forgetting a supporter of Nintendo's systems and if I am I will add it here.