Compact Flourescent Lightbulbs
Replacing just one 60W bulb in your house with a compact flourescent bulb could save $1 BILLION with a "B" per year, if everyone in the US did it.
I knew compact flourescents were way more efficient, but that's some crazy math. We use one in our dog's room, for an exterior light just outside our basement door, and have more to replace other exterior lights once the current bulbs burn out.
We've found they just don't work for living spaces, though. I put one in our family room light for a night, and the light is just so, well, flourescent. Makes my brain hurt. Still, I'd think most people would have somewhere that one would make sense. They also last much longer, and don't generate the heat of a regular bulb.
[via kottke]

That's an extra billion dollars I can then use to cover for rising gas prices when filling up my 8mpg Minivan!
Supposedly, the headaches that some people get from florescent lighting is more a result of having more than 1 tube in a room. The flickering of the multiple bulbs is never in synch, which causes light levels to pulse at weird intervals.
Gomez 21 Jun 2006