Carrie Williams at Boyd Elementary recently showed us how a Wii remote (~$45), a USB Bluetooth adapter 
(~$20), a Radio Shack switch, a few plastic tubes, several rubber bands, and some free software can be made into a fully-functional smart board.
That is Carrie in the photo holding her homemade pointing device. We’ll post video soon of the demonstration she recently gave for the district media specialists – it is really remarkable stuff.
In the meantime, see the guy who started it all on YouTube – Johnny Lee – present his ingenius Wii remote hack at last year’s TED Conference: