Super-awesome facial rigging tutorial by David Ward, available now at BlenderCookie.com! Â This tutorial teaches you how to rig an alien face: head, mouth, and eye - even how to do "sticky eyeballs." :)
From the BlenderCookie.com page:
This tutorials covers how to create a more advanced type of facial rig, showing you how to use the â€œstretch toâ€ constraint to give the face a more fluid way of animating. The â€œstretch toâ€ is great for things like lips and eyelids (which is shown in this tutorial); in addition, I show you how to make the eyelids â€œstickâ€ to the eyeball surface, so there's no unwanted gap between the two while animating.