I recently returned from a trip to Washington D.C. One part of that visit was discovery of Jack Rose Dining Saloon, 2007 18th St NW, Washington, D.C.
They have over 2400 whiskey choices, and the largest single malt collection I have seen anywhere. You can get some idea of it by looking at the Whisk(e)y menu on the website. But, the online menu only tells part of the story. A very knowledgeable bar staff, and they feature both one and two ounce pours, with clear pricing for each.
I found out about this great location through the Single Malt Whisky Society list of bars that include SMWS drams on the menu. Indeed, that portion of the menu is impressive.
If you find yourself in Washington D.C. with a little free time, and you enjoy whisky, I would recommend finding your way here. I was fortunate to be in the neighborhood just as they opened, it is clear that they fill up quickly, so if you plan to add in food you may want to make a reservation.