Update: More information about this topic is posted on the TechPsych blog.
I'm working with a few students who have multiple special needs who are in need of assistive communication technologies that are not expensive. Although my first idea was to look at eye gaze technology, the possibility of face tracking is also appealing. Take a look at the following video from SeeingMachines, a commercial company:
I have a couple of webcams, and I don't mind a trip to RadioShack. I can program a bit, too, but I have very limited time. I welcome any advice you might have.