One of my favorites is Great Wall in Chelsea on 25th and 9 Ave.
Although the majority of their food is cheap and mediocre at best, the Singapore Chow Mai Fun is seriously good (spicy curried thin noodles with shrimp, chicken, vegetables and pork) as are the wonton and hot/sour soups. They also have pretty decent fried chicken (yes I know its not chinese at all) too.
When I'm having a bad day or when money's tight - this so works for me. I'm sure there are others Chowhounders out there that have hole in the wall chinese favorite food places too and would love to hear about them.
239 9th Ave, New York, NY 10001