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I found this through a friend the other day. This program Facegen is amazing. It doesnt cover all races yet, but you can dial in things like how male or female a character looks, the proportions of the forehead, cheekbones, lips everything. I know this was originally intender to be 3d software but I think that anyone wanting to understand the human head would be interested. Go to http://www.facegen.com to download the demo. It's worth it! Best of all, its almost completely photo-realistic
Heres a couple pics as an example, you can also do caricatures if you want.