![Image](http://makezine.com/images/tools/fretlight.jpg)
I actually have one of these. A novelty to be sure but it did show me how to play some songs in real time. I teach my guitar students with it.
![Image](http://www.geeky-gadgets.com/wp-content/uploads/2012/03/tabber.jpg)
Tabber is interesting but way too geeky for me. Nobody wants to play a guitar with wires all over it.
![Image](http://hackadaycom.files.wordpress.com/2011/07/guitar.png)
ColorChord is software that rects to the vibrations of your guitar. You can assign a different color to every pitch. Where you put the LEDs is entirely up to you.
http://www.youtube.com/watch?v=o_i6bse7SKw
Just a Thought: If I could put any assigned color into my fretboard (12 pitches = 12 colors) and then have it react to my playing style in real time it would make for a pretty awesome spotlight solo don't you think?