A green plumber friend of mine recently told me about a toilet that he has been recommending to a lot of his clients.
Basically, it has two different flushes. One for number one and another for number two. They use different amounts of water so that you are not flushing the maximum necessary down the drain every time you use the bathroom. It does not cost significantly more money and you are helping the environment in a bigger way than you know. Water conservation is an important issue that gets bigger every year.