sustainAgility

If you don't know about hyper-milers, this is a good place to start.
Tips for improving gas mileage 30% or more (via  Philadelphia Inquirer | 04/24/2008)

According to Mr Rubin and Treehugger the gas stations of our future may need to team up with local chiropractors to get that crick in our backsides fixed.

Hyper-milers, though a little extreme at times, have developed  some practices which could be adopted by less enthusiastic folks. For instance, removing roof racks and/or extraneous weight from the trunk, like your golf clubs.

Wikipedia

Driving Tips:

www.fueleconomy.gov lists official EPA mileage ratings for most cars and trucks from the 1985 model year on.

www.cleanmpg.com has detailed tips from top hypermilers, including Wayne Gerdes, who is widely credited with coining the term.

www.ecomodder.com, Benjamin Jones' how-to site for people willing to modify their cars to boost mileage.

www.ecodrive.org takes a global look at driving for mileage, and points to European countries that now require ecodriving instruction.