67 Mott Street
Chinatown is, of course, the premiere spot for both cheap and expensive Chinese food. The dozens of restaurants are both universally good and (to my Western eyes) virtually indistinguishable.
Big Wong is my favorite old-school Cantonese place in the heart of Chinatown. Food is simple but good, and cheap...as long as you order from the regular menu and not the "Special" (aka tourist) menu.
Next: The Halal Guys