Several years ago we installed a programmable thermostat. It has lowered our heating bill almost 30% over the last few years. We have seen a 20% reduction in cooling costs. This really adds up. The best part is that we don't even notice any difference in our house, the temperature only changes when we are not home or asleep.
This winter I installed insulation on the hot water pipes in our basement. I haven't tracked how much we are saving, but it cut the time to get hot water by a third. This makes a big difference in how much water we were wasting waiting for the hot water. The water is also hotter at the faucet. This was well worth the $10 and 1 hour investment.
Think of all the things you might keep plugged in that you might not really need. Have an extra fridge? That might be costing you as much as $30 a month! Take a quick look around you house and you might be able to find those little money vampires.