FYI -
There are two airports in the metro DC area. IAD is NOT Reagan airport. IAD is Washington - Dulles International Airport and it is in Chantilly, Virginia which is about 20 miles west of the city. There is a Marriott almost walking distance from the terminal - the Washington Dulles Airport Marriott.
DCA is Ronald Reagan National Airport. It is located in Arlington, VA and is right across the river from the city. There are numerous hotels right by DCA in Crystal City - which is the "neighborhood."
Which airport are you flying in and out of? Make sure you don't go to the wrong airport - it happens all the time here. Also, I would just look for all the big chains and check near the airports. I would imagine many of the hotels will have a park and fly - esp near IAD. IHG, Marriott, Hilton, etc.