Here's another few sites to check out:
http://www.lovecastle.org/draw/ (Has heads-only gesture drawing)
http://eyedrawthings.com/?page_id=3 (lots of good facial expressions)
http://www.pixelovely.com/gesture/figuredrawing.php (gesture drawing)
Obviously drawing from life is best whenever possible. But seeing as how we don't always have an army of models waiting to be drawn, photographs can be helpful.