As the current light bulbs in your home burn out, replace them with compact fluorescent light bulbs. They use less energy, which helps the environment, and also helps save you money on your electric bill. Also, these bulbs last much longer than the regular variety, so you won't need to replace them as often. Look for bulbs labeled "Energy Star."
According to Energy Star's Web site (part of the EPA and Department of Energy):
"If every American home replaced just one light bulb with an ENERGY STAR qualified bulb, we would save enough energy to light more than 3 million homes for a year, more than $600 million in annual energy costs, and prevent greenhouse gases equivalent to the emissions of more than 800,000 cars."Visit Energy Star for more information about these bulbs.
Bonus tip: Looking for an excuse to buy that flat screen TV? According to this article from the Scripps Howard News Service, an LCD flat panel television uses less energy than the older, bulkier varieties. But choose LCD or rear projection over a plasma, as the former two use less than half the energy as the latter.