The RMI Cool Citizens Guide lists a number of things you can do that are absolutely free, yet could save you hundreds of dollars in a season.
1. Lower water heater temperature to 120°F
2. Increase AC thermostat by 3°F
3. Wash clothes in cold water
4. Air dry clothes during summer
5. Turn off unneeded lights
I should note that turning your water heater down to 120 is a controversial bit of advice, particularly north of the border. Both the Canada Safety Council and the US Department of Labor recommend that the water heater be set at 140 degrees to eliminate the risk of Legionnaires' Disease. Read about it in TreeHugger: Is it Safe To Turn Down Your Water Heater Temperature?