Adafruit makes neopixels in a variety of shapes (https://www.adafruit.com/category/168). The smaller rings and sticks make good ornaments. Put some fun on your tree with these programmable RGB LED lights.
Step 1: Wiring
For easy hanging, each ornament is wired independently with 4 wires, two for power, one for input, and one for output. Twist thin green wire together and it will disappear into your tree.
This little breakout board connects an arduino to the first ornament and chains the other ornaments together. For instructions on how to wire, see https://learn.adafruit.com/adafruit-neopixel-uberguide .