I lived in DC for just about a year and September would be a nice time of year to visit. One of the biggest reasons is that most kids are back in school, so they aren't in the city on their tours. It's a pretty cool town. We liked going to Old Town Alexandria and The Chart House on the Potomac for dinner, the The Fish Market for schooner of beer. We liked Georgetown for restaurants, too.

There is so much to see in that city. If you can, get a hotel near a Metro station and skip getting a car. Unless you have time to take a ride out to Annapolis.