If you've been thinking about getting a more fuel-efficient car, you might enjoy checking out
www.fast-math.org where you'll find a new converter that just showed up today. You can enter the number of miles you drive per year, the mileage your current car gets, and the mileage of a vehicle you might buy, and see how much you'll save per year. This works for hybrids, as well as things like gasoline vs diesel trucks. You can also use it to runs as-ifs, and after-the-fact comparisons.
Have fun!
- Jeff