Instrumentation such as a ScanGauge or UltraGauge is the most helpful mod. It helps you "adjust the nut behind the steering wheel". I bought a ScanGauge about 11 months before I found ecomodder.com. Enjoy your ScanGauge. It makes fuel economy a fun game.
Synthetic lubricants can also help. If your engine calls for 5W-30 try switching to a 0W-30 synthetic. I switched to Mobil 1 0W-30 synthetic in my 4.0 last oil change. I had been using Motorcraft 5W-30. I gained about a half mile per gallon - not a dramatic difference, but noticeable. It will also save me money on oil changes, since I can safely extend my oil change interval to 12 months (about 8500 miles).
One mod I did in May was installing an underdrive crankshaft pulley. It frees-up some power (and economy) by driving the accessories (particularly the water pump) 25% slower. It also reduced rotating mass by 25.5 ounces. It's an expensive mod ($300+) and I gained about 1 MPG with it, so it'll pay for itself in fuel savings in about 80,000 miles.
When you're due for new tires, you may want to consider Low Rolling Resistance tires. I found the Yokohama YK580, which is the unlikely combination of high performance, low rolling resistance, and fairly high treadwear rating of 580. They're rated for 130 MPH. I bought them on July 8, so they're still breaking-in. I also went one step up in diameter (235-60R17 vs 235-55R17) to reduce my cruise RPM. This required re-calibrating my speedometer, which I accomplished with my Hypertech power programmer.
Power programmers are a bit expensive, but they give a boost in power without affecting fuel economy (in my experience). They can also be used to reprogram shift points and shift firmness in auto transmissions. As mentioned, they can also re-calibrate the speedometer for changes in tire diameter and/or gear ratio.
If you're able to limit your freeway speed to 65 MPH, it can make a big difference in economy.