Last December, I ripped out a page from Business 2.0 about the Power-Cost Monitor. It's a little piece of technology that attaches to your electric meter and then displays on a monitor in the house. It shows you how much you're spending per hour and you can watch it go up and down as you run the dishwasher or the air conditioner.
I recently stayed at a friend's house with one of these devices and must say I'm convinced that the studies have it right. When you can see what it costs, people spend less. For the first time ever I didn't turn on the lights to take a shower in a guest bathroom flooded with morning sunlight. For every family that's ever debated what it really costs to leave the lights on and whether it's more expensive to leave them on or turn them off and on, this is this year's must have Christmas gift.