Step 4: Go on now, haunt your house.
By now you're already thinking about strobe lights, bottle rockets, and ceiling fans. Or hell why not strobe the whole damn house? If you want to interface with high voltage AC, you're on your own, but let me recommend the Sharp S216S02 Sold State Relay. Here's some features:
~ Minimal current. Unlike magnetic relays, these use an internal LED to make the magic happen. Use a high value series resistor with the + or - pins!
~ Zero Crossing. That means when it turns on, the High Voltage side of the circuit waits until the AC wave crosses 0V. No joke. I don't know how it works either. Something to do with a Triac and/or a Diac or maybe a Dalek. Doesn't matter. This will not work on any DC circuits! RTMFDS!
Have fun! And if you can't be safe, be careful.