In my reptile rooms I only use 3" heat tape which isn't all that much to run. However, when I went around the house I got looking into other non-reptile ways I could reduce the power consumption of the house as a whole.
One of the things I did was go out and replace about 75 light bulbs with energy efficiant compact flourescents........the ones that fit into the incandescent light sockets. Here is how the bulbs break down:
9-11 watt Flourescent = 40 watt incandescent
13-15 watt Flourescent = 60 watt incandescent
20 watt Flourescent = 100 watt incandescent
The light output is the same but the wattages are very reduced. It cost me about $300 to change all the light bulbs over, however, it is saving us 2500 watts in power that we use all the time every day (lights that we use outside, in the bedrooms, family/living rooms as well as the hallways, kitchen....etc).
These bulbs are also rated for 10,000 hours where as an incadescent one is rated in around 2000 hours. If you buy the bulbs in a pack of 6 at Building Box they will cost you $25 which with tax brakes downs to in around $4.75 per bulb. It says that over the life of each bulb they'll save you on average $40-90 in hydro bills.
I'm sure their are other ways to reduce the power consumption of the house, but I just haven't gotten that far as of yet.