For the Christmas of 1999 I designed and constructed a computer controlled light show for my dorm floor. (4 North)
After toying with some prototypes, I decided that a simple relay with transistor driver system would be manageable, and be dirt cheap to implement. The final project ended up using 5 double gang boxes in the north wing, with each box containing two switched circuits. The control signals were daisy chained straight through the boxes back to a PC parallel port, which generated the pattern signals. So a total of 10 switched circuits down the length of the hallway, and synchronized music at some times, created an awesome effect that still amazes people today.
What you can't see in the video is that we had a nearly identical system in the other wing, except that it used 6 boxes instead of 5. (The other wing is two doors longer.) In all over 30,000 lights were strung on 4North that year.
Note that I didn't develop any of the patterns. I just gave Brad Martin a shared library to control the lights and he took it from there.
Here are the insides. You can see the transformer which supplied power to
the relays, the perfboard which contained the circuitry, and the two wall
receptacles. The entire cost of all parts including the interconnecting
data cable was around $17 a box.
Blurry picture of the circuit board. Need a better camera.