We use a lot of energy in the kitchen, and unfortunately a lot of it is wasted. Stove tops release most of their heat energy into the air, and large ovens heat more area than is required. Refrigerators are constantly releasing heat into the kitchen, but rarely are able to do it efficiently. And there's always the problem of dishwashers -- while they are generally more water efficient that hand washing, they use more energy. But here are some things you can do to reduce your energy usage.
When cooking on the stove top, cover up! You lose a lot of heat in the form of steam and heat radiating off the food. A lid can help foods cook faster and water boil more quickly. You may also be able to turn off the burner before the food is done cooking, and let the residual heat finish the job. Many people cook pasta by bringing it to a boil and then turning off the heat, letting the pasta cook in the cooling water. Hard boiled eggs can be cooked this way too. This works especially well if you have a well-sealed pot, keeping the heat in for longer.
You can also save a lot of energy by cooking in an microwave rather than a stove or oven. The microwave deposits heat directly into the food, resulting is less wasted energy. Electric kettles are much more efficient (and quicker) than boiling water on the stove top. Crock pots also save energy, even taking into account the longer cooking times. Rice cookers and pressure cookers are also good energy saving devices.
Use as little water as you can for cooking. If you are boiling water, there's no reason to heat up more than you need! If you're making tea, you can measure the water into the kettle one mug's worth at a time, resulting in exactly the amount of tea you need. Pasta needs enough water to circulate, but the pot doesn't need to be full. When in doubt, measure short. You can always add more water later.
One good way to save energy and stay healthy is to eat foods raw. This may involve acquiring new tastes and exercising your jaw a bit more, but raw vegetables are just as healthy as steamed (often even healthier), and much healthier than boiled.
Refrigerators have to radiate heat to do their job. This heat generally radiates from the top and back. Unfortunately, we usually place the fridge right up against the wall and pile things on top, effectively insulating it and making heat loss difficult. Moving the fridge away from the wall and keeping the back and top clear will help it work more efficiently. Obviously, your fridge should not be right next to your stove, and it'll do better if you keep it out of direct sunlight and away from other heat sources. Keeping the coils clean is also important, no matter how unpleasant the task is. They are underneath or on the back of the fridge, and even a simple vacuuming every few months can help greatly.
Even harder, keeping the fridge closed will help. Especially difficult for those of us who have kids, but it may help to have snacks that can be eaten at room temperature, like fruit, snack bars granola, candy fruit leather, etc. Also remember that you have control over how cold your refrigerator and freezer gets. Don't set them to the highest setting unless you have a special reason to do so.
Don't put hot foods directly in the refrigerator! Package the cooked food however you like, and then leave it to cool to room temperature on the counter. This will keep the fridge from having to cool down all that extra heat, and it will also prevent the hot food from warming up other food in the fridge or freezer, which will have an effect on food quality.
Some of these things seem small, but these are things that we can do every day, sometimes multiple times a day. Multiply the smallest of these by 365, and you start to see noticeable changes. Saving energy will generally save you money, and it will also help prevent the pollution of our atmosphere, the mining of land for coal, and the use of food crops for producing biofuels.
If these actions are not enough for you, there are also certain food choices that save energy; Vegetarianism, Veganism, and Locavorism, for example, can reduce the amount of energy put into producing our foods. Other things a hardcore hippie might want to try include haybox cookers, solar ovens, earthenware cooling devices, and rocket stoves. And for the rest of us, there's always cooking with your car engine.
rootbeer277 says re Conserving Energy in the Kitchen: Cool, but can I get a source on the microwave information? I've always wondered whether or not it's really more energy efficient. (That information can be found here, or here if you want to do the calculations yourself.)
For the freezer, I use ice cream as a temperature indicator, if it scoops easily without getting melty, the freezer is at the right temperature. If it's a brick that bends your spoons, it's too cold.
Kit says re Conserving Energy in the Kitchen: For the sake of food safety, food should be cooled as quickly as possible if it is to be stored. Leaving it on the counter to cool may allow it to be in the "danger zone" for too long, and grow bacteria. I work in a grouphome for people with disabilities, and we are required to follow strict food-safety regulations. We cool our leftovers in small containers in icebaths before sticking them in the fridge. The small containers cool faster than leaving the food in the serving dish, since they have less thermal mass.