UPDATE: Updated purchase links so that they work.
We all use computers (obviously), did you know the average computer uses between 150-350 watts of electricity to run? Well, I found out a computer maker who keeps the environment in mind and makes a desktop computer that uses between 5 and 20 watts of electricity to run! Huge difference.
Click here to purchase this incredibly efficient desktop
Under $200 and comes with gOS which is Googles version of Linux basically. If you don't like it, you could easily get Ubuntu or Kubuntu and install it over it. Don't use Windows please. You don't "need" Windows no matter how much you think you do.
Be sure that if you purchase the above desktop, recycle your old desktop. There are a number of computer recycling centers around the country.
Apple Computer Recycling
Dell Computer Recycling
General Electronics Recycling
Google Search for "Free Computer Recycling"