Today I received the X-Rite M50103 ColorChecker (Grayscale). Even though I've had it for just one day, I wanted to mention how much of a top-notch product this is.
Here is a sample of the card against one of our backdrops. This has been lit with our two AlienBees strobes, 45° angle from camera-center on both the left and right-hand sides. Click on the image for a larger view:
From left-to-right are the following:
And here's an example being applied to a subject:
This card works very well in my Lightroom workflow. I really like that it's a larger size than my old pocket-sized cards, making it easy to get a feel of the light being thrown in its direction. It's also large enough that it's easy for people to hold in the photo, but not too large to where it would be awkward.
I'd recommend this to anyone that wants to improve the color quality of their photos. Purchase yours on Amazon.com.