I threw this up here largely because it's been so long since I've posted anything. It took about 20 minutes from start to finish and is obviously not intended to be representative of polished work. Each "portrait" here is about 1.5 inches square.

It's a useful exercise (although to get the most benefit from it, you should do entire body poses and not just the head), and if it takes you longer than half an hour to draw twenty expressions, you don't know your character well enough. Keep drawing! :)