After trying simply to cool down my office at home I went back to the Carbon Calculator at Al Gore's site and realized a shocking thing.
My energy usage (at $125-150/month) causes approximately the same CO2 emissions as my car, which has a super inefficient V8 engine.
I live in an apartment, run the A/C a bit, and have lots of computers. But the CFL (compact fluorescents) have made such a noticeable difference in the temperature of my office (and as a result I actually run the A/C quite a bit less). With a 5x decrease in energy usage and heat, it seems crazy not to use them everywhere.
As I've said in other posts, these are not your father's fluorescent lights. I hate the old fluorescent, color-shifting 60Hz stutter. Instead you can get warm lights at halogen (3000K) or incandescent (2700K) color temperatures, and they look great, don't flicker, and they're even dimmable.
I replaced my old incandescent desk lamp with this full-spectrum one (which has great contrast for reading), and I replaced my 300W Halogen torchiere with this one and a Halogen-temperature bulb, a combination that looks pretty incredible. The new lights are really well made too.
You don't even have to go that far - simple replacement bulbs will work with your existing fixtures.
And the impact of this is not insignificant. It's almost as if I've bought a Prius for $100. The CO2 impact of all this is huge, the new bulbs last forever (10x longer than incandescent), and it's really very easy to do this yourself.