This is something I've pondered before. I asked about one gesture on yahoo answers long ago. All I got was a guy saying that even he didn't know the term for it (it was the gesture where someone holds something in front of them towards someone else to indicate that they want the person to take it).
But the one I'm thinking about now is describing a posture people assume when they're nervous (the kind of nervous where say someone is in a place that scares them for whatever reason). They cross their arms and place their hands on their upper arms. I think they also put their legs together (at least, girls do). I can't really think of an efficient way to express this.
Its kind of annoying we don't have simple words for these gestures like we do for some facial expressions. We have words for to smile, to frown, to scowl, etc... but we don't have a word for showing an anxious expression.
Has anyone made a list of efficient ways to describe gestures and facial expressions? It would be quite handy.