Turn off the lights in the rooms of your house that you are not occupying. Make it a habit to flip the switch each time you leave a room. Save electricity and save on your bill.
Install CFL (or, even better, LED) bulbs wherever it makes sense. These bulbs might cost more initially, but they both have a longer life than normal incandescent bulbs and they both eat far less electricity.
Lower the temperature on your gas water heater. You really don't need water heated up to 180 degrees. Lower it a bit and save.
Simulate a Low Flush Toilet: If you don't have a new, water-saver toilet, you can simulate one by putting a clean brick, or a sealed plastic bottle filled with pebbles, or a weighted mason jar, into your toilet tank.
Insulate! Insulate! Insulate! Check the weather stripping around doors and windows. Caulk or foam insulate any place where outside air has a chance to get in. Don't forget to insulate your attic floor with either "roll" or "loose-fill" insulation.
Reevaluate the stuff in the rooms in your house. Go into a room and go through every single item in it. Do you really need that item? Are you happy that itís there, or would you be just fine if it were not? If not, get rid of it.
If you have a security system at home, call your insurance company and let it know. Many will give you a discount on your homeowner's insurance and may even refund part of your last premium.
A good tip for your clothes dryer: Check the lint trap and clean it weekly. The dryer will run more efficiently saving you money and energy.
Wash and re-use zip-lock bags. They last forever!
That spare refrigerator can use up to $300 per year in electricity. If you are using it, great. If it has only a few things in it, try to move them to your main fridge.