If sometimes you find your writing going stale in this area, here's a resource you may find useful:

http://thebookshelfmuse.blogspot.com/2008/01/introducing-thesaurus-thursdays.html

The Emotional Thesaurus lists all sorts of gestures and reactions that may help fire your imagination.

I'm sure it isn't as good as people watching first hand but if you are stuck for differing gestures and can't get out and about in the real world, this is a good second.