I’ve made a small (portable) led matrix for testing new code. It is powered through USB so there is no need for an additional power supply and common ground between the controller and the leds.
http://www.youtube.com/watch?v=6Qw4qBPUB5Q
solves a problem! now you can code in front of the tv without the missus complaining about “all your electric junk all over the place”
maybe that’s just mine :-/
lol, that’s exactly why I made it! 
the only thing i would change, is to get it running from a teensy, and then attach that to the back of the card. then its just one cable from the computer to the unit. will look tidier and less cluttered.
although mine is just a full 5m coil nailed to a block of wood… so my advice is less worth