...and someone really ought to point out that the Lilypad Arduino is pretty good-looking all on it's own, no enclosure needed.
I kind of like the look of the Diecimila and NG boards in the open, too. My Diecimila has a dark blue soldermask, so along with the green soldermask of the ultrasonic sensor and the red soldermask of the motor control board, mounted on my bot's shiny tin deck, well, all I need are some decorative color-shifting LEDs I guess:)