Power down your computer
The "sleep mode" reduces energy use by 60 percent to 70 percent, the EPA estimates. As for turning computers on and off, despite a popular misconception, this won't harm the equipment. It will, however, save energy as long as the computer will be inactive for 16 minutes or more. If your job doesn't require constant computer use, break the habit of turning it on first thing and keeping it on all day.
When "Mr. Electricity" Michael Bluejay calculated two extreme examples of what it would cost to run a computer -- one high-end computer that's left on 24/7, and one that uses less energy to begin with and runs just two hours a day -- he found that the first would cost $405 a year to run. The other? Just $5.50.