Here are some more interesting facial expression reference sites.
This site is is 2D which I think makes it easier to see the facial movements. You can also select combinations such as the eyes up or down or the mouth - smile, sneer etc. You'll need Java to run this one.
This game allows a player to experiment with the different effects of moving separate facial parts. In teaching someone how a face conveys emotion, you may choose to isolate one part, such as turning brows down to indicate disapproval, or up for surprise.
On this site, you pair up the eyes and the mouth. It' interesting to see how the mood of the face changes with only four choices of eyes and mouths.
Here, you can download videos of various expressions. The videos have an overlay analysis of the movement of the underlying facial muscles. You could use this analysis to help you determine the various morph targets of your facial mesh.
I found this this site interesting in that you control a robot's expressions by moving your mouse over the controller.