Hotel George
The Hotel Helix
The Hay Adams
Willard Intercontinental Hotel
The Watergate Hotel - arguably Washington, D.C.'s most famous hotel is currently undergoing extensive renovations and sweeping for the odd listening device and will not be accepting guests until some time in 2009.
Blair House - the worlds most exclusive hotel. The invitation must come from the worlds most exclusive home. The White House's guest house for past and future US Presidents, world leaders and other dignitaries.
C-Span hosted a one hour special this past weekend on Blair house, which you can view here.