I’ll recommend once again this hotel in Arlington. It’s 3 minutes’ walk from the Virginia Square metro station, which means you can be at the Smithsonian museums, the Capitol, the Zoo, or any other downtown DC destination in 15-25 minutes. There’s a mall and several restaurants within walking distance (including a cheap all night pizza and sandwich place next door). I lived a block away for several years.
It’s not luxury, but it’s decent and relatively cheap accomodations.