Late night eating on Friday night near the Watergate shouldn't be too tough. There's Sequoia just a block away ((202) 944-4200 - 3000 K St NW).. also for a nice neighborhood bar with food there's Marshall's ((202) 333-1155 - 2524 L St NW) just a couple blocks away. Really, though, you have all of Georgetown to choose from.
As for Sunday brunch, please see the
Washingtonian's Guide. Are you looking for anything in particular (area of town? price range? atmosphere?)
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More Room Throughout Coach: the Website of Free Miles and Free Markets