Some time ago I wrote a blog post titled Getting the most for your gas dollar. When I started tracking my miles/gallon on my cars I was curious to compare what others who had similar model car get on their cars. Then when I was reading forums on wesabe.com (good web site to take control of your finances and provides budgeting tools, personal finance tips) I came across someone mentioning fuelly.com – exactly what I was looking for.
Fuelly is a site that lets you track, share, and compare your gas mileage. Simply sign up, add a car or motorcycle, and begin tracking your mileage.
To start tracking mpg on your cars/vehicles, you will need to register your car(s) with information like make, model, year and other information. Then periodically as you fuel up your cars you will need to enter these information in fuelly.com – think of fuelly as a log book 
Once you got a couple of fuel-ups you can start seeing your reports when you login to fuelly.com – they give you a dashboard view. Here is a my dashboard at fuelly.com – can be accessed at http://www.fuelly.com/driver/the8thwonder/
Fuelly.com does have links to browse similar cars – that way you could see how others rank with similar car as yours 
Also checkout Fuelly’ tips – http://www.fuelly.com/tips/
