That's what what katecm was talking about...it's called Off the Record...and i agree i had one there that was really tasty and the atmosphere is cool. Dinner at the Lafayette room after was the perfect 'nightcap'.
Have not had one of their "classic" martinis, but the frou-frou ones (yes, what was I thinking) are delicious, large, and well-proportioned (alcohol-content-wise). Though, the vodka-tasting is much more fun! :o)
Round Robin bar makes good classic drinks. Of course Todd Thrasher is the best bartender in town, but his cocktails you want to be non-traditional. There was someplace my brother who loves martinis, but prefers gin, really liked for a plain dirty martini, it might have been Zola.
You don't have to stray too, too far from Dupont to get to Off the Record, where the bartenders are excellent and, to be honest, it's a bar where looking around makes you want to drink a martini.
I am hoping not to start a debate about what does and does not constitute a martini, but since drinking gin is like work: Vodka martini, up, cold, olives.