One of the best graphite portrait artist's that I know is Brian Duey. Brian has a comprehensive series of drawing tutorials on his website: http://www.dueysdrawings.com/drawing_tutorials.html. I highly recommend these tutorials as they are clear and concise. I frequently reference them in the art yahoo groups that I moderate and I personally refer to them anytime I am working on portraiture. Check out Brian's artwork and see if you agree with me!