If you haven't already, get a soil test done. It's easy and costs a crummy ten bucks. See the pages at the link below. The test results will tell you what your soil actually needs to properly support your lawn. Most of the stuff that TV commercials push will simply wash away into our creeks, runs, and streams, and eventually Chesapeake Bay. The fewer chemicals you add the better, but it certainly does help to add what's actually needed -- particularly lime if your soil is on the acidic side, as it will be if you have lots of oaks and dogwoods around. All that will be in your soil report. Otherwise, aeration followed by top-dressing every third year or so will help a lot. That's a good time to overseed with a hardy mix of quality seed as well. Occasional watering during dry spells will help also, as will keeping your mower blade sharp and not mowing the grass too short.
http://www.soiltest.vt.edu/