When I was a graduate student at Montclair State, one of my professors brought in a former student who was working on a headset that would be controlled by brainwaves. The application that he had in mind was for users with physical disabilities who could not control a pointing device such as a mouse.
This was the sort of thing that I immediately thought would work great with gaming too, because as a child I dealt with a little pain in my thumbs after playing Nintendo for a while (we called it "Nintendo thumb").
Well, apparently some of the hardware developers had the same idea, as the world's first brain controlled gaming headset is available! Very cool stuff, with a price around $300.
Link to article (with pictures!)