Use solid-state relays to blink the lights on your Christmas tree in time with music. Also good for Halloween haunted houses.
Step 1: Acquire and Set Up a Christmas Tree
Get a nice large, healthy tree set up in front of your biggest windows. See How to Pick and Decorate a Christmas Tree for more details.
Step 2: Add lights
String lots of lights onto the tree. Use as many sets as you like, but arrange them such that there are three light regions, each with a separate plug. Run these three plugs down the trunk so they can easily be attached to the light controller. Up to three strings of lights can usually be linked in series, so you can almost certainly cover even big trees.
Step 3: Hook me up
Plug light strings into the controller you built for Halloween: http://www.instructables.com/id/Solid-state-Halloween-controller-and-how-to-build-/ Attach computer and sound system. Select high-quality Christmas music and sync the lights with a winamp plugin: http://www.8-legs.org/ewilhelm/projects/2.165/index.html