Here's a face rig that I created around two years ago. Its was a bit of a prototype, but i think it works quite well and is worth posting. It uses some nurbs shapes for the major parts of the face, and drives joints attatched via some hair follicle nodes. Nothing too fancy. The face for my Jedi character is based on the same type of rig, though that character has improved control of eye deformation and more control of the mouth region.

The animation below was done by Gary Talbot, a top animator at Rare.

One of the requests for this setup was that animation could be shared across rigs easily. This is acheived, in this instance, by manipulating the nurbs shapes and fitting them to the required face. Then its a case of reconnecting the joints of the face. Below is a test for this, though it has some issues it proved the concept would work across faces of different proportions and styles.