Going digital with a model that automatically changes the indoor temperature setting is fairly easy, and it can trim about $180 off your annual heating and cooling costs. Simple models that only control heat are sold at home centers for around $25. But units like the one shown here can handle many more functions, including cooling and humidifying. Typically they're purchased through and installed by HVAC contractors, but you can get a good deal on one by buying online and install it yourself in no time.
Cost: About $475.