Live eye tracker with a cheap webcam
Cubic Motion usually apply their computer vision technology to high-end footage, but it can be applied to all kinds of data. Watch their youtube channel for iPhone and Android demos, coming very soon.
Below you can see a 60fps face tracking system, which can be used for live character animation system for Maya, Unreal Engine, etc. 60fps facial feature tracking from head-mounted cameras. Obviously not as precise as offline data, and it still makes a few small mistakes here and there, but should be excellent for previz.