For Greek food, try Symposium, 112th or 113th between Bway & Amsterdam (warning--sometimes they close for a summer vacation). Also, on Amsterdam between 122/123 is a row of restaurants: Sezz Medi, Max Cafe, Turquoise Grill, Kitchenette, and Max SoHa. I'd recommend all but Turquoise Grill.
For a cheap slice, try Koronet on Broadway and 111th. For upscale-ish diner food, there's Deluxe, Broadway and around 113/114.