A few months ago, there was a flurry of activity connected with the "camera" inside the Wiimote...
This little beauty apparently is relatively easy to extract (the Wiimote costs about $15), and put to our own wicked(?) purposes.
It is not JUST a little "camera"... it has a whole lot more: It "watches" a scene, and finds the four most "noticable" "blobs" it can "see", and returns to the rest of the system the x/y position of each of the blobs. With an IR filter in front of the sensor, it only sees sources of IR; take the filter away, and it can track bright lights.
If the sensor is on a fixed support, it can be used to monitor the movement of bright lights in its view. Alternatively, it could be fixed to, say, a robot. If it operated in a controlled environment, and in that environment you provided some fixed lights, then your robot could infer its position by the "movement" of the lights... etc, etc... It would be perfect for my seismograph project, for instance.
I'm snowed under with various things at the moment, and am hoping that someone with more energy will feel like making up something like what is described at the letsmakerobots site mentioned in a moment. If they do, I'd be interested in buying it from them later... $40? (Subject to inspection, of course.) (You have the fun of "playing" with it along the way, anyway!)
The best write up I've seen is at...http://letsmakerobots.com/node/7752
Arduino software at...http://www.stephenhobley.com/blog/2009/03/01/pixartwiimote-sensor-library-for-arduino/
More good stuff at....http://blog.makezine.com/archive/2008/11/hacking-the-wiimote-ir-ca.html
... and elsewhere.
(If you want to embark upon building one for me, and don't want to be "stuck" with "Oh, thanks, but I already got one from someone else" at the end of the day, please send an email to me at the email address you can collect fromhttp://sheepdogsoftware.co.uk/contact.htm
... subject line "Wiimote commission". I can pay in US dollars or GBP.)