See the bottom of this page for a sortable list. Things keep changing so I still need to keep compiling and verifying data but what I've found is available here in semi-random order. Hopefully this helps make it easier for you to make educated decisions on which providers to use for buying, converting, and viewing films.
Official UltraViolet providers list
Disc to Digital
(DVD to SD & HDX, Blu-Ray to HDX)
Windows XP+ w/ Adobe Flash & AIR
Mac listed one place but no D/L link?
At Walmart stores
Streaming
Windows (Flash 10.3)
Mac OS X (Flash 10.3)
Linux (HAL & Flash 10.3)
Android 4.0+ (SD-only & w/ Adobe AIR app?)
iPad (SD-only)
Xbox 360, PlayStation 3 (SD, HD, HDX)
Blu-ray player
Smart TV
Roku, NeoTV & similar set top boxes
Download
Windows XP+ w/ Adobe Flash & AIR
Android 4.0+ (not to external storage)
Streaming
Windows (Flash 10)
Mac OS X (Flash 10)
Linux (HAL & Flash 10)
Streaming
Xbox 360 (only 1 UV account - no household sharing)
Set Top Box
iOS 4 Device (iPhone, iPad, iPod Touch - SD-only)
Android 2.2+
Windows 8 app (ARM, x86, & x64)
Windows XP+ (Silverlight, SD & HD)
Mac OS X (Silverlight, SD-only)
Chromecast
Apple TV
Download
Windows (Silverlight)
Mac OS X (Silverlight)
Set Top Box?
iOS 4 Device (iPhone, iPad, iPod Touch)
Android
M-GO (U.S. only)
Streaming
Windows XP+ (Widevine & Flash or Intel AppUp - SD+HD)
Mac OS 10.5+ (Widevine plug-in or Intel AppUp)
Smart TV (SD + HD)
Some Google TV devices (SD + HD)
Android 4.0+ (Tablets only)
iPad w/ iOS 6+ (via Safari)
Roku
Download (not available yet)
Windows 7 (M-GO Download Manager & Silverlight)
Windows 8 app?
Streaming
iOS 5.1+ (iPhone, iPad, iPod Touch)
Android 2.0+
Windows XP+ (Flash 10.3)
Mac OS X 10.5+ (Flash 10.3)
Linux (Flash 10.3 & HAL)
Google TV 2.0+
Xbox 360 (US-only)
Ouya game console
Windows 8 app
BlackBerry (?)
Amazon App Store (Kindle Fire, etc.)
Download
iOS 5.1+ (iPhone, iPad, iPod Touch)
Android 2.3+
Windows XP+ (Microsoft .NET Framework 4 & Adobe AIR)
? -> Mac OS X 10.6.8+ 64-bit (Adobe AIR)
Disc to Digital
Windows XP+ (Microsoft .NET Framework 4 & Adobe AIR)
(DVD to SD & HD)
Streaming
iOS 4.0+ (iPad, iPhone & iPod Touch via Safari)
Windows XP+ (Silverlight 4)
Mac OS X 10.4.11+ (Silverlight 4)
Download
Windows XP+ (Silverlight)
Mac OS X 10.4.11+ (Silverlight)
Streaming
Windows XP+ (Flash 10.3)
Mac OS X 10.+ (Flash 10.3)
Android
PlayStation
Xbox
Smart TVs
Blu-Ray players
Download
Windows XP+ (Windows Media Player 10, CinemaNow plugins & Adobe AIR)
Android
Mac OS X 10.6+ (Adobe AIR 3.5)
Disc to Digital
Windows XP+ (Windows Media Player 10, CinemaNow plugins & Adobe AIR)
Mac OS X 10.6+ (Adobe AIR 3.5)
Stream & Download
NOOK HD or HD+
Android
iOS 5.1 and later
Roku app
Movie studio info site
Download
Kaleidescape systems
Target Ticket (beta):
Streaming
Windows (Flash)
Mac OS X (Flash)
Android
iOS devices
TV & game consoles "coming soon"
Download
Windows
Mac OS X
Download
Windows XP+
Cineplex (Canada):
Streaming
Windows XP
Smart TV
Blu-ray
iOS devices
EzyFlix TV (Australia):
Download
Adobe AIR for desktops
Streaming
Windows 7
OS X 10.7.5
iPhone & iPad (iOS 6)
Android 2.3
a bunch to add here
blinkbox (UK):
more to add here later
MovieStop & FlixFling
Upcoming TBD
Upcoming TBD
Upcoming TBD
Not all titles are available with all providers because of differing licensing deals
Not all provider's content are available in all locations where some restrict purchasing by location & others do it for viewing too
Can't stream on jailbroken iOS devices or rooted Android phones
Most if not all HD viewing requires a fully HDCP compliant connection
Many providers offer non-UltraViolet content like TV, Disney & other content
Xbox requires Xbox LIVE Gold membership
Linux distros with newer architectures won't support streaming easily since Flash's DRM requires HAL (per comments from Adobe employees in a forum thread & Flash's Tech Specs/Reqs) which is deprecated & being phased out