Ikea has for some time sold a white plastic box filled with christmas-tree lights, that hangs on the wall.  I have for a couple of years now thought about replacing these with a matrix of individually-controlled RGB LEDs.  This simple device could be used for so many things:

• This device could be used to show aiosphere network function, with different colors for gateway and wireless end points.
• It could show a clock, in a variety of forms.
• It could be used as an extremely low-res still-image display (or video, but Zigbee is not a good network choice for this).
• It could be a lamp.
• It could be a color-organ or mood lamp.