BCD binary clock using blue LEDs, though you could use any color. The case is laser cut out of bamboo plywood. The sheets are about 3mm (1/8") thick.
The custom controller board is an embedded Arduino Duemilanove. There is an ATmega328P, DS1307 (ugh), and a TLC5940NT. The TLC5940 is overkill to drive the LEDs but makes it possible to do some nice fading effects easily.
I am not a fan of the popular DS1307. As long as you do not need the chip to track time, it is a great real-time clock. While powered it loses a couple of seconds per day and on battery it loses minutes per hour.