One of the best-kept secrets in NYC (secret from tourists, that is) is the Burger Joint.
The entrance is almost completely hidden behind floor-to-ceiling, Oz-like velvet curtains in the lobby of the upscale Le Parker Meridien hotel. The Burger Joint is the exact opposite of what you'd expect to find in a luxury hotel - this no-frills dive features graffiti covered wood paneling, cheap vinyl seats and a cluttered, shack-like environment. It's a tiny, hole-in-the-wall spot for burger enthusiasts.
Go for the fun, offbeat experience of it and order their signature burger "with the works" and crispy fries. It's a cheap thrill - burgers are about $8 - but go off-hours otherwise you'll stand in line. (Another alternative is to call ahead for pick up.)
Also, cash only!
119 West 56th Street