Don't speed. Driving over the speed limit can severely cramp your miles-per-gallon and your pocketbook. The difference between 60 mph and 80 mph is $900 in gas expenses per year (assuming 500 high-speed miles driven per month).
Drive slower and you'll also save 225 gallons of gasoline annually. On average, each five mph you drive above 60 lowers your gas mileage by about 2.5 mpg. In addition to the obvious reduced risk to your safety and driving record, sticking to the speed limit will also save you the time it would take for 15 additional fill-ups per year.