I would say Fairfax in Virginia. It's about a thirty minute drive to Washington D.C. It's a great alternative to staying in D.C. And you'll have easy access to all the DC sights and attractions. Here's a great resource for Washington DC attractions.
I like to stay at the Marriot Courtyard in New Carrollton MD. It has parking, is in walking distance of the Metro and AMTRAK and has a quiet rural ambience
www.newcarrolltonmaryland.com
www.newcarrolltonmaryland.com