To date my favorite burger in NYC is Minetta Tavern's Black Label Burger, although the $28 price tag doesn't allow me to splurge too often. Last weekend while on the Upper East Side my girlfriend suggested we try J.G. Melon. It was around 2:30pm so we only had to wait five minutes. I won't go in to much detail about the history of the place, although it probably deserves a spot in the Oldest Establishments thread.
The burger was a close second to Minetta. Nothing fancy about it; great char on the outside, a juicy medium rare on the inside, melted cheddar, a few pickles/onions, all for $11 (see pic below).