Stay the course on 2nd and 3rd avenue but head north to the 50s and you'll find a TON of places to go. As you go up on street numbers, you'll go up in drink prices though. Still, if the dark (not dim), lounge type atmosphere is what you crave, here is where you'll find it.
The first is Mica Bar. This Oriental-laced decor full of plush chairs and leather couches is a lounge to model lounges after. You will pay for drinks exactly what you expect by the look of it. It's a popular post-happy hour place, even on weekend when the commuters steer clear of the city. Oddly enough, it also has happy hour appeal, due, in part, to the reduced happy hour drink prices.
It's not crowded and is quite trendy. It's great for after work with the happy hour specials and and social scene. Their martini selection is great.
You will see mixed reviews about this place depending on the night but one thing that almost everone will agree on is that the rooftop bar is great. It's not exactly on the roof. more like a roof that opens. Great idea. Wildly popular.