Johnny Chung Lee pretty much shocked the entire video game world (and lots of others) with this video (5.8 million views, 5/5 star rating with 21,000 votes):
This is a pretty nifty bit of engineering, using the off the shelf Wii Remote and a relatively cheap extra (safety glasses with IR leds <15$) to provide a very high level virtual reality setup.
Secondly Nintendo has recently come out with the Wii Balance Board. This peripheral can accurately measure your weight distribution.
If we combine the potential of head tracking with weight distribution it would be possible to create a very accurate Matrix-style dodging bullets experience, simulating what is seen in this clip:
This would be a damn sweet feature if integrated into a full action game. It could likely be accomplished with head-tracking alone, but the combination of board, head-tracking, and Wii Motion Plus makes for near full body integration. The Matrix franchise is perfectly positioned to take advantage of the technology, seeing as everyone wears sunglasses in the movie anyway.