If you are the type of person who is dedicated to saving as much energy as possible you'll get a charge out of Blackle. Blackle is the energy saving search engine powered by Google's search technology.
Created by Sydney Australia based Heap Media, Blackle uses a black homepage which they argue saves energy because your monitor uses less electricity to show a black screen or webpage. They say that using Blackle to do your searches will step by step save quite a bit of energy over time.
Whether you think this might be obsessive compulsive or a bit of fun saving a tiny amount of energy the real motivation behind it is to remind people to do what they can to save energy.
Here's the homepage of Blackle.
Info on Heap Media.