One way to save money is to think double. If you're going to run the oven, especially on a hot day when the oven use is going to push up the AC bill, don't run it just for a single item.
In the simplest form, if you are putting a chicken, turkey, or roast in the oven, put the vegetables in with it. My mother always added potatoes, carrots, onions, and, sometimes, mushrooms to the broth surrounding a roast. And frankly, those were some of the best vegetables I've ever had. But it also saves on extra dishes and pans and saves the energy that would be used to cook those vegetables on the stove top or in the microwave. You can bake potatoes in the oven while other things cook as well, which saves the cost of microwaving them (and I like them oven-roasted myself).
Even better, put some bread or a cake in the oven to bake at the same time, and get twice the use from the electricity. For example, tonight I have a casserole baking in the oven, and I put in some bread to bake at the same time, essentially getting the bread baked for free.
Another approach to this is to cook up a lot at once to freeze. We do this regularly, mostly with meats. If we buy a lot of chicken on sale, it gets baked in the oven all at once, and most of it is then cooled, cut up, and frozen for future meals. I also roast two or three packages of hot dogs in the oven at the same time to freeze for my lunches. But if you like homemade breads, you can bake several loaves of bread at the same time, especially if you have a larger family.
But don't limit this idea to saving on energy while cooking. Buying something new? Think multi-use, like a swiss army knife (but don't get suckered into buying a gadget that does a dozen things, but all of them poorly). Decide whether getting a specialized gadget is really necessary for you with two questions: Does it really work much better than an ordinary hammer, or whatever? And will you use it often enough to make it worth the investment?
For instance, a special mallet with spikes for pounding meat DOES work better at tenderizing than pounding it with an ordinary weight of some sort. But if you're only going to use it once every 2 or 3 months, is it really worth the extra cost and storage space? The same for a double boiler (sp?). Yes, the fancy thing works best. But you can nestle a metal bowl over a couple of inches of water in a sauce pan and do about the same thing, and the metal bowl and sauce pan can be used for lots of other things. However, we've found spending the extra $2 or $3 to get a real corkscrew is MUCH easier than trying to remove a cork with the one that's part of the bottle opener.