If you own a home, solar water heating is the smartest investment you can make. Solar water heating is cheap and will pay for itself really quickly. Depending on how expensive natural gas is (it gets more expensive every year), it can pay for itself in 3-5 years. That is really fast. Remember that there is a 30% (and going down) subsidy from the government for solar.
Here is a modern looking one. I make no claims for how efficient it is. I just like how it looks.