I was recently in the market for a new car, and I found myself constantly switching back and forth between Craigslist and fueleconomy.gov because I wasnted to see what the gas mileage was like on the cars that were for sale. Suffice to say, this was tedious. So I developed a tool that allows me to see both the Craigslist ads and the fuel economy ratings of the advertised cars in one place. The tool is available for free at http://fueleconomy.weblite.ca.
See the press release here.