Kotobuki for terrific sushi. It's on Nesconset Highway in the ShopRite shopping center. Nearby, Pace's Steak House is quite good. A little further north, in Saint James on Route 25A, you'll find Kitchen, a Bistro. Wonderful, inventive food.
Branchinellis in Hauppauge is definitely some of the best pizza on Long Island. Pollos Mario in nearby Brentwood for Columbian. Luso in nearby Smithtown for Portuguese including all you can eat rodizio.. Yummy!
An enthusiastic second for Branchinelli's. For breakfast or lunch, Maureen's Kitchen in nearby Smithtown. Love Kitchen a Bistro. I've only heard good feedback about Luso's. Cafe la Strada, too, consistently good reviews for many years, noted for wine list.