Interactive TV Related Consulting (& More)
(Services and websites vary with time. Please verify.)

One way to find out about an entity's involvement with interactive television is to type both their name and "interactive tv" in search engines.

3Vision
eOne
Accedo
Accenture
Activision
Adobe PrimeTime
Amino
Alticast
Arris
Ascent Media
Allin Interactive
Arlen Communications
ATSC
AXMEDIS
AWARN
A Different Engine
BBC Research & Development
Bill Niemeyer
Breakaway Communications
Brightcove
BrightLine
Broadband TV News
Broadcast Projects
Bsquare
Cadent
Canoe
Cartesian
Celerity
Comscore
Concero
Concurrent
Connekt
CTAM iTV Metrics Committee (PDF file)
C&W Business
Devoncroft Partners
Digital Slate - Virtual campuses incorporating interactive TV.
Dimetis
DMX Technologies
DTV Innovations
Ensequence
easeltv
ESPIAL
Excentis
ExtendMedia (CISCO)
Farncombe
Federal Hill Communications
FourthWall Media
Furture Reality
Futarque
GCT-ALLWELL
GoldMedia Consulting & Research
GoTV Interactive Technologies SA
Harbor Research
HbbTV
IAB
IBM (IBM Interactive Television)
Icareus
IGDTV
Infosys
IfThen Digital
IMG
Informitv
Interactive Future
Interactive Television Alliance
Interactive TV Works
IPV
[itvt]
Kodi
Oliver & Ohlbaum Associates
Massive
MediaGeniX
Microsoft Advertising
Momentum
mufin
Mx1
My Interactive TV
NCC
NDS (CISCO)
NetRange MMH
Neotion
Ocean Blue Software
Ooyala
Openet
Orbit Interaction
PACHEM KOREA
Park Boulevard Productions
pjb Associates
Perception2
Proxama
RadioactiveGiant
Sapient Interactive
SeaChange International
Sematron
Sentosa Technology Consultants
Silicon Artists
SimpleBox
Simplestream
Sorenson Media
Spiderdance
Spotmagic
Strategy & Technology
Stoneroos Interactive Television
Streaming Video Alliance
Switch Media
Tara-Systems
TechXcellent
Telescope
Teleste
Telestream
The Digital TV Consultancy
The Myers Group
ThinkAnalytics
THINKFARM
Tmira Solutions
Tracy Swedlow
TransGaming (Gaming - Oberon Media TV)
Tru Optik
TSS Cross Media Group
tvstrategies
UniSoft
User Vision
VideoClix
Viaccess Orca
Video Storm (NetPlay)
Vimond Media Solutions
Vision Strategies
Watchwith
Whitney Quesenbery
WizTiVi
You.i TV
Zappware
ZeeVee
Zenterio
Zodiac Interactive

Worth Checking:

3RD Sense
Ad-ID
Alphonso
Anchor Worldwide
ANT Limited
Applied Broadband
ATG BROADCAST
Avaya
Betting Corp.
Blum Interactive Media
Boolean Consulting Ltd
Brainjuice
Broadcast Projects
Broadcast Traffic Systems
Canadian Media Producers Association
Ceres
CMW Interactive
Couchman Communications
Dalet
David Gary Studios
Diamond Multimedia
Epic Signal
eProcess Solutions
Flipside
Hulu (Interactive Interstitial)
IBM iX
icrossing
ICSI  (International Computer Science Institute)
Interactive Media Peer Group
IT Convergence
MX1
Motorola Developer
NAB
NorDig (Platform for Digital Television involving the Nordic region)
Openet
Paratel
PearlTV
Peer5
Publicis Media
Public Media Company
Rick Howe - The iTV Doctor
Sarbakan (Gaming with interactive TV)

SaskTel International
StoryTech® Immersive
SuperAwesome
Tangent Interactive
Tegna
Television Academy
The Vertere Group
Tindara Group
Trilogic
UBI
Videology
Videa
VisionConsult

Xlent
XML.org

Related Market Research and Analysis

Barb - A major source of TV audience data in the UK.
BBC Worldwide Labs
Datamonitor
davita
Digital Tech Consulting
eMarketer
Econsultancy

e-Media Institute
Ensequence - Audience measurement & more.
Fairfield Research
Forrester Research

FourthWall Media
Futurescape
Gartner Communications
GoldMedia Consulting & Research
Gracenote
IHS Markit
Horowitz Research
iSpot.tv
Inscape
Interactive Future
Interactive TV
Invidi
Leichtman Research Group
Lotame
Marcus Evans Company - A business events and information company.
Market Research Reports
MediaBiz
mufin
Nielsen Social
nScreenMedia
Ovum
Parks Associates
Phil Leigh's Inside Digital Marketing
Practical Marketing Analytics
S&P GLOBAL MARKET INTELLIGENCE
ShareTracker
Spirent Communications
The Carmel Group
The Diffusion Group
The Media Audit
TVTime
United Business Media - A business events and information company.
UITV.info -Interactive TV Research
User Vision
Verimatrix
Wainhouse Research
Watchwith
Zenith Media

An Early History of Interactive Television