According to the EPA, a programmable thermostat can save as much as $180 over the course of a year. Basic models can be purchased for as low as $25 - though you'll probably want to hire a professional to install it.
Steve Marcus/Reuters/File
A Trane ComfortLink II thermostat is displayed in Las Vegas in this 2011 file photo. Programmable thermostats reduce bills by optimizing your energy use, and can save up to $180 per year.