Tips for saving energy and staying cool are the subject of this article over at Martha Stewart's body+soul online magazine. Energy expenditures often rise dramatically in the summer, especially in the city, where it can be harder to get a cool breeze.
In the kitchen, they suggest cooking outside or in a toaster oven to keep the kitchen cool, and to save energy. What else are you going to do when it gets too hot to cook? This sounds counter-intuitive, but we actually eat a lot of braises and soups in the summer. It's just so much cooler to let something cook covered on the stove than to heat up the oven. And of course there's going to be plenty of fresh fruit and icy things!