I bought a book some years back titled Building Believable Characters. It’s put out by WD, and not a bad book at all, but it is a little cliche. It contains a list of behaviors, then gives a long list of facial expressions, demeanor, gestures, etc. to fit those behaviors. The problem was that those expressions, etc. could fit other behaviors as well.
Like James, I think people watching is the most effective research tool for seeing the different ways people react to the same types of situations. I also think that writing nonverbal cues is intuitive- as you write and get to know your character, you automatically know what their reaction will be.