For the upcoming all-CG Robert Zemeckis movie Beowulf, the animators used a process called Electrooculography ("OEG") which maps the actor’s eye movements, down to the eye-lid flutters.  They place three sensors on the skin around the actor’s eyes that pick up electrical pulses given off by the eye muscles and surrounding nerves. 

The result, I think you will agree, is pretty damn impressive. The overall animation is pretty mind-blowing too.
 
http://www.apple.com/trailers/paramount/beowulf

Daryl Brewer