Stop using Google and start using Blackle. Based on the idea that a black screen uses less energy than a white one, it will also act as a reminder to keep taking small steps toward saving energy every time you search in black.
Hopefully you've already heard about it and are using it, but we found it worthwhile enough to spread the word some more. We're looking forward to when they come out with Bmail or even better, Blackmail. Go here for more information, and start blackling!
Update: Blackle is only beneficial on CRT monitors not on LCDs. See this Wall Street Journal article for the run down on the numbers. Either way, it's an interesting concept and should serve as a reminder that every little thing can help.