Rooftopbar The Ides, which is on the 6th floor of the (very popular) Wythe Hotel. Please do let me know if you think there is a bar with a better view on Manhattan.
Since New York Times Style magazine The Ides highly recommended it, it seems pretty hard to get in to. We were there on a Sunday afternoon (a bit early, around 3 or so) and could just go up. They don't have a dresscode and are open every day. If you go there, please tell Carlos and Teresa behind the bar that the Newyorkcitytrippers send their greetings. Oh and supposedly you're not allowed to take pictures. Don't worry and just go ahead, everybody takes pictures there anyway.
The Ides is on the 6th floor of the Wythe Hotel, 80 Wythe Avenue in Brooklyn. Take the grey L and get off at Bedford Avenue.