Over the summer I watched as my PSE&G bill just kept creeping up and up, until I decided to do something about it. See, over the winter I'm lucky because heat, cooking gas, and water are all included in my rent but A/C is part of the electricity - meaning I have I have pay for that during the summer months.
In my apartment I had one of those old school thermostats that cannot be programmed, so I ventured out to Home Depot, picked up a programmable thermostat and installed it myself. It was a quick and easy change that costs me about $30.00 (since I didn't need anything too fancy) and since I installed it myself I saved there as well. Since most people have to pay for heat and A/C it would be especially beneficial to make the switch.
Note: If you are renting make sure you save the old thermostat so you can take your programmable one with you when you move.