Here's a tip on a small tool that offers huge production value in a variety of ways, but it will require you to have a Mac system with a thunderbolt connection. The Blackmagic Design Intensity Extreme is an HDMI / Analog Capture and Playback Device. In this video (below) i'll run through just a few examples of how I personally find value in this product.
First, the Intensity Extreme offers 10-bit capture from your HDMI. It's definitely not as portable or as convenient as an Atomos Ninja, but if you already have a Macbook this is a great entry level way to start capturing higher quality HD out of your camera - including the Canon 5D Mark III.
Blackmagic Design Media Express Capture Software
Second use for me is as an interface for my camera(s) to Live Streaming services. We've actually used this feature to send a wireless HD signal from a mobile camera. The camera is free to move around, and the wireless HD video (connected to Intensity Extreme via Thunderbolt) streams live out to the internet. We've also connected our HDMI 'Program feed' out from a switch to the Internet.
WireCast Live Streaming for YouTube
My favorite use for the BlackMagic Intensity Extreme is to use my Macbook as a professional HDMI Preview Monitor. While you can see a live video feed through other software, ScopeBox by Divergent Media takes this feed and applies professional overlays and scopes. The interface is extremely flexible so you can add remove scopes, resize windows, or even go solo full screen. The image from my MBR (retina) has colors that I expect to see when it's time to edit. The resolution and pixel density allow you see your images clear and sharp.
Using Macbook as HDMI Video Preview Monitor with ScopeBox Software
Even if you can find another large 1080p lcd screen (television), you will need a portable power source and a way to transport the screen. Not to mention the problems you'll run into when working with various resolutions and framerates. If you've got a MacBook available, there's no simpler way to have yourself a professional portable battery powered monitor that's easy to transport by purchasing an Intensity Extreme for less than $290 dollars. Keep in mind that you don't need a beastly Macbook. The Intensity Extreme does all the hard work and can be used with even a lightweight Macbook Air which has amazing battery life.
You can find additional information about the tools mentioned in this article through the links below.
BlackMagic Intensity Extreme Thunderbolt HD/SD Capture
ScopeBox high quality highly flexible preview monitor
Seaport Digital i-Visor Cases
[Note:] As pointed out by a commenter, you can get most of this functionality with a cheaper BlackMagic Design UltraStudio Mini Recorder Capture Device. The reason I went with the Intensity Extreme is for the additional features it offers including an HDMI output which I use for my various setups. If all you need is to input your feed to your computer, check out the BlackMagic Design UltraStudio Mini Recorder Capture Device (here)
BlackMagic Design UltraStudio Mini Recorder Capture Device