The Coding Horror weblog details how to determine the cost of running your PC all day, then describes a few ways you can cut down on your power consumption and lower your bills.
To determine your power draw, the author suggests either buying a tool to measure your energy consumption or, if you don't feel like shelling out the cash, you can make an educated guess. Then you can just plug your numbers into the equations to determine how much power you're computer eats every year. Finally, the author suggests some methods for cutting down on your daily consumption, like setting your hard drives to sleep on inactivity. Whether you keep your computer running all day or not, these tips could help you cut down on your computer costs.