I was looking at building one of these a while back for my computer. It seams pretty easy with an Arduino, a $15 roll of RGB LED strip and some computer software. Though going beyond computers, it gets quite complicated.
http://blinkstick.com/ was on here a couple of days ago too, it can be wired in to a Ikea multicolour LED light strip (I forget the name) - their demo video shows it synced to display colours.