Hi stevewww - welcome.
You've already hit some of the big topics: proper maintenance, max tire pressure, reduced speed on the highway.
Some instrumentation would be nice to help you fine tune your driving style even more, but of course you already know your car is a year too old for a
ScanGauge. A SuperMID may be an option however.
At the very least, I trust you're calculating your fuel economy on every fill? You should consider
adding your car to the Ecomodder garage so you can post your results for all the world to see. It serves as a good reference point for people to help you, and as a motivator too.
Other than further refinements to your driving style, I'm with Daox. Aero mods are most likely to help based on your commute profile. Head over to the aerodynamics forum and check the sticky:
List of aero mods you can do to your vehicle
Looking forward to watching your progress.