If your hot water heater is 10 years old or older, get a blanket for it. Like this one.
New models are well insulated and don't lose much heat. Not sure if yours needs one, touch the tank and if its warm/hot to the touch it needs one. My newer one (4 years old) is cool to the touch.
I've also heard good things about timers for hot water heaters, but have never looked into getting one. It wouldn't work for our family anyways, the water could be used at anytime of the day or night with 14 people living here of all different ages and lifestyles.