Don't squander the heat in your waste water
You pay to heat water for your shower, yet up to 90% of that heat (heat equals energy) ends up going down the drain along with some of your precious, precious hair. According to an article in Business Week, the heat we squander in wastewater equates to $40 billion a year (even more in households with several teenagers).
Among the companies that pose a solution to this loss is RenewAbility. Its Power-Pipe product cleverly captures heat from the gray water and uses it to preheat water entering your home from your water supplier.
The company claims that its product can be installed for $600-$1200, and will yield a return on investment of 15-50%, four times the cost efficiency of solar power. While I'm always uneasy with figures that posit such a quick payoff, the idea of reclaiming the heat I've paid for makes a lot of sense to me. If you're looking for ways to shave your energy usage, this or a similar product might be worth a look.