If you don’t have one already, you really should get one. Now they even have ones that you can control with your smartphone!
Try a programmable thermostat
Heating and cooling accounts for almost half your energy bill – about $1,000 a year! A programmable thermostat is one of the easiest ways you can save energy in your home and help reduce carbon pollution. An Energy Star qualified programmable thermostat helps make it easy for you to save by offering four pre-programmed settings to regulate your home's temperature in both summer and winter - when you are asleep or away.
Learn more about saving energy at home: http://www.energystar.gov/index.cfm?c=products.pr_save_energy_at_home
Here’s the Consumer Reports buying guide to programmable thermostats - http://www.consumerreports.org/cro/thermostats.htm