Electrical lights burn up a lot of money. I only buy compact flourescents now. They do a great job for 1/4 the energy burn. CFLs are pretty cheap now, too.
Motion detector switches help too. I use those outdoors, due to crime and our border security (thanks Bush).
We had a sound activated switch for the garage door once. When we approached the house and activated the garage door, the light went on. Then it went off later. Kids loved opening the door to the garage and shouting, turning on the light. We donated that switch to our niece and nephew.
Actually, that brings up an intersting point. Is there any truth to the urban legend that actually turning on florescent lamps uses more energy than running them for an entire day. In grammer school, I had a teacher that would flick the lights on and off to get our attention, until she discovered that that was not green-friendly behavior.
And when you combine them with CFL, in cold weather the lights come on slowly to give an intruder a chance to get away..