While researching an earlier story about global warming (and I wish I could recall which story it was, so I could link to it), I mentioned this site: Carbonfund.org
By going there and calculating your "carbon footprint," you can donate to Carbonfund.org an amount roughly equal to the dollar value of a "carbon credit" for our usage. This offset will be used to advance alternative energy research, technology and implementation to reduce carbvon emissions.
You'd be tempted to "buy" your way to a polluting future, but the system works such that the less carbon you emit, the less you have to donate (by the way, this is effectively the individual application of the Kyoto Treaty. By paying for your carbon emissions, you assist others in leapfrogging carbon emissions altogether, or at least implementing cleaner energy generation, which is more expensive, until alternative energy scales down in cost.)
In addition to this, most utilities now offer some form of "Green Power" purchasing. Sure, it costs a few bucks more, but the way gas and oil prices are rising, that differential is being wiped out quickly. So far, I've bought wind power and solar power. Once New York City institutes the tidal force generation they've toyed with, I will purchase that first and foremost.
All this is in addition to some simple things you can do around your house: buy mini-fluorescent bulbs instead of incandescent, and for heaven's sake, shut down the computer and air conditioning when you don't need them. Unplug the "always in standby" appliances that you don't use daily. Walk or bike to the corner store for that gallon of milk. You know all the stuff, you don't need some jackass lecturing you on a saturday about it.
But I wanted to post a reminder that, as we get into the silly season of blackouts and brownouts and rolling outages and heat and humdity, it's more important now than ever before to save energy and to save the earth.