Custom Holiday Lights
Make your own holiday light strands using these lights from Adafruit (http://learn.adafruit.com/12mm-led-pixels/overview).
Included above are designs for 9 unique bulbs and the LED holder that will allow the LEDs to fit snuggly in the base of the bulbs. You will need to drill 5/8" holes in the bottom of each bulb so that the LEDs can stick up into them. I use a print setting that prints a 2 layer shell with no interior fill.
I've also included modified code from Adafruit that programs all the lights to continuously randomly change their colors. Make sure to install the utility files from Adafruit in the Arduino libraries directory.