During an energy audit an expert sizes up the efficiency of your appliances, air and heating systems, and gauges how much air your home is leaking. Replacing incandescent lights with compact fluorescent light bulbs, using a programmable thermostat to control when air conditioning or heat turns on can whittle away at your utility bills. "Adding attic insulation is a good energy saver that does not break the bank," notes John Ritterpusch, assistant vice president of sustainability and green building at the National Association of Home Builders. Adding high-efficiency toilets can also translate into savings, especially when you factor in potential rebates from water utilities that range from $25 to $200, according to the U.S.