DiffShade (single channel)
This channel is a grayscale image that shows the results of the Diffuse lighting and shadows on your objects.

SpecShade (single channel)
And this channel is a grayscale result of the Specular "hits" the scene's Lights create upon your surfaces. I sometimes use this instead of the Specular Color buffer when creating "blooms" glinting off bright metal.

Motion (single channel)
Motion is used by some specialized tools that can create pretty convincing motion-blur, in real-time, in your compositing application. (The ones I've worked with are still in Beta, so I can't make suggestions for which I'd recommend... yet. :)