3
Circles Media
3RD Sense
Activision
Arkadium
Atari_Interactive
Artech Digital Entertainment
Betfair TV - Betting application for TVs running the Yahoo!(R) TV Widget Engine.
Betting Corp. - Offers gambling via interactive TV
BUZZTIME
Dhruva Interactive
Digita Oy
Digital Animations Group
Eidos Interactive (Studio)
Endemol - Television programming developers and creators of interactive TV games.
EuroGamer - Large gaming website
Exent Technologies
Frima Studio Inc. 
FUN Technologies plc 
G4 
Gala TV
Gamasutra - Gaming web magazine
Game Developer Web magazine
Games4TV - Iacta
Gamez
GameHouse - Gaming web magazine.
GamePlay - Web retail gaming outlet.
GameSpot UK - Web retail gaming outlet.
Game Show Network Interactive (GSN) - Huge interative gaming network.
Gaming Industry Stocks - GamingIndustryStocks.com: an investor and industry news portal for the gaming sector.
Global Interactive Gaming 
GO Real Time Animation 
GooMe Interactive Ltd.
GSN - GSN is a huge US cable/satellite network devoted to games and game shows. GSN offers interactive television.
Hasbro Interactive 
Icareus 
IGDTV 
IGN Entertainment
Infogrames Interactive (Formerly Hasbro Interactive)
In-Fusio - Mobile gaming.
Intent Media - MCV 
iTV Gaming Watch - Data, analysis, forecasts and success stories on the interactive digital TV gaming market. 
JPM Interactive 
Levels Newsletter - A newsletter for game developers.
NDS
NetPlay TV - Large UK interactive TV gaming concern.
Netscape Navio Navigator
Oberon Media
PacketVideo
Personal Java
PixelPlay Inc.
Planet Xbox - Gaming site
Playcast Games-on-Demand 
Playin'TV - A major interactive TV gaming channel.
PlayJam Interactive TV Games - PlayJam is a huge interactive TV games channel.
Pop Monkey Productions
Prizemo 
QueenBee Interactive 
Rearden 
RedLynx
Rule Web Development
Sarbakan
Sega (& Sega Dreamcast) - Interactive TV Gaming.
SinglePoint - SMS.
Sky Games 
Slingo, Inc.
Stoneroos Interactive Television
Sveng.com - MHP Games.
Tempt Destiny Game
Tetris
TransGaming
TvHead - Interactive TV gaming.
Two Way Interactive Entertainment
Two Way TV - Interactive production company that creates and distributes cross media TV shows and games.
Ubisoft - Producer, publisher and distributor of interactive entertainment products.
UDcast
VADIAN.NET - SMS TV.
Visiware
Winner Channel
Xbox365 - Xbox presents the opportunity for interactive TV.
Yahoo Games on Demand

Click here for a huge list of Games Developers

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Various Related Definitions:

Broadband Gaming Console
Communal Gaming
Gaming-specific Broadband Service
Global Interactive Gaming
In-Game Ads, In-game Advertising
Interactive TV Gaming
Interactive TV Game Show Participation
Mosaics (TV)
On-demand Gaming
Online Interactive Gaming
Roleplaying Games (RPGs)
Set-top Gaming
Sex-themed Gaming
Video Game Player

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Related:
The 3rd Generation Partnership Project (3GPP)
Digital Game Developer
Levels Newsletter - "The Art & Science of Game Development"
Spectrum: Interactive Media & Online Developer News
Wireless, Interactive TV and Online Gaming- Screen Digest