British Gas - iPhone app has a button to turn on the camera light when submitting a meter reading.
/via Jaik Dean
Blom and Blom - All the lamps on the website light up when you hover them.
Special note: Blom and Blom are friends of us here at LBD and are true design connoisseurs of the physical world. They will also be featured in our sidebar as a reminder that good design details are not just important on your screen.
Lion Safari - The scrollbar changes the color depending of the background of the current website. (dark or light)