Colorchecker Cards etc.

How many of you use the Colorchecker Cards, Grey Cards, WB Cards etc and where can you pick them up for relatively cheap?

I think the best grey card I ever bought was the one inside the front cover of the National Geographic field guide to Photography.
I personally use a piece of gray ripstop held tightly over the end of the lens, on MF, with wich I shoot a custom gray shot for my custom setting just like the guys with the 100 dollar expodiscs do. Pretty darn close, definitely closer than the flourescents and overcast settings on my particular camera.
Shoot Raw.

I just picked up a whibal. From my little use of it, I like it a lot. I just include it in the first shot of a set and in PP I have an accurate reference.

Grey Card who uses one and which one ??

Gray Card…White Paper. What’s best?