The University of Buffalo's VR lab has developed a cap for your index finger that is exquisitely sensitive to movement--to the point that it can actually be used as a 3D digitizer. It has an accelerometer, a force sensor, and a motion tracker, and its developers believe it'll hit the market in three years, which is admirably conservative--usually researchers predict (and it's always hubris) that they're only one year away from their first Ferrari.
First, I want no lame jokes about communicating with the computer using your center digit. With that out of the way: This device is exciting mostly because of cell phones, which currently have at least two disadvantages in the UI department.
First, their keyboards are tiny. Second, in most cases, you have to unholster them in order to use them. Of all the frustrating, clumsy things to do! What we've always needed is an input mechanism that leaves our hands free, and this cap is pretty close. It's not too hard to imagine a standard gesture language (think of handwriting recognition systems) that would give you access to a wide variety of smartphone functions. Output would come to your headset (I'm happy to observe that many Bluetooth headsets are being worn even when their owners aren't on the phone. I regard this as creeping wearable-ism and a Good Thing.) If you wanted more input bandwidth, you could put caps on several fingers and communicate using some variation of American Sign Language (Thad Starner at Georgia Tech has shown that this is feasible. Perhaps you'd make an old-fashioned rotary dialing gesture to enter numbers; if the virtual dial were big enough, your precision wouldn't have to be very high. (Of course, you'll look ridiculous standing on a street corner making broad, circular arm gestures for no apparent reason, but you are an early adopter: You know that all progress extracts a price.) All in all, potentially pretty cool. I hope it turns into something.