If your home has a traditional, non-programmable, thermostat where you just "set a temperature", you should replace it at once. Programmable thermostats allow you to set multiple times during the day where you can change the set temperature. The advantage of this is that when you need the house warm, it can be warm. And when you don't need the house warm (when you are sleeping under the covers or away at work), the house can be cooler. This results in big savings in your energy bill, not to mention a big reduction in the amount of resources that you use.

These thermostats are relatively cheap at $50. They can easily save you that much money in one month by allowing you to use less energy without making your house any less comfortable.