I thought I'd post this here instead of the painting section because figures are the most likely to be painted in gray scale as opposed to planes, tanks, and space ships!
Read an article in an issue of Amazing Figure Modeller( # 43) about painting figures in gray scale. I've always wanted to do the Aurora monsters using this method but didn't know which colors to use.
The author of the article suggested this color pallette.
Duplicolor Grey Primer
Folkart- 480 Titanium white
613 Charcol grey (I couldn't find this one locally, maybe discontinued?)
479 Pure black
Americana- Grey sky
Slate grey
Delta Creamcoat- Charcol
Citadel- Codex Grey
I've found that different companies have different ideas about what color "charcol" or "black" is supposed to be!
Read the post on "paint charts" in the Painting section for conversion tables if you cannot find a particular color.