Buy an Offset
Carbon offsets are the big thing right now, because they're easy and they might actually make a difference. They basically work like this: You pay for enough clean power (wind or solar, typically) to cover the dirty power you use. People buy them to offset travel, home power usage and any other energy-heavy expenditure.
If you're busy and you have some extra funds, this could be a great way to celebrate Earth Day. Just decide what you want to offset -- it could just be your home-power usage for Earth Day, or you could take the opportunity to offset your car travel for the whole year. Just go to one of many Web sites (type "carbon offset" into your browser to find a whole slew of them); use the Web site calculator to figure out how many offsets you need to buy; type in your credit number and you're done.
Up next: Speak your mind.