On a hot DC day, I suggest snagging a table or spot at the bar on the Donovan House rooftop for brunch.  The view of Thomas Circle is lovely and the restaurant area is next to the hotel's pool which appears to be fabulous.

I was very excited to try Jose Garces' new restaurant, Rural Society, in the Loews Hotel.  One thing DC really lacks is a plethora of restaurants that serve brunch on Saturday.