Well maintained car, change oil every 3,000 miles or so. Mostly highway driving.
Removed the factory mud guards. Installed a ScanGauge II (2/26/11) and have been using that to improve my fuel economy.
I started car pooling 3/28/11, so my car's fuel economy is not as impressive (at least on the surface) as it used to be, but I am saving lots of gas and $$! I have had two passengers commuting with me each day since March 2011.
Since June of 2011, I have been over-inflating the tires by 3 psi. At first I was skeptical that this would make any real difference, but it did boost my fuel economy noticeably, so I've continued that practice.
I'd like to add an extension to the front air dam and attach flush panels to the underneath of the car. The air dam would need to be removable since I often drive through deep snow in the winter.