Turn off your computer at night. A recently released study conducted by Stamford, Connecticut and the Alliance to Save Energy, (a Washington, D.C., coalition of business, government and environmental organizations) found that in the US alone, energy waste by PCs adds up to $2.8 billion.

Additional Resources

http://www.scientificamerican.com/blog/60-second-science/post.cfm?id=leaving-pcs-on-overnight-wastes-bil-2009-03-30

http://ase.org/