Post theater dinner-W 45th
Agree that Marseille is a good choice.
Another always reliable spot is Trattoria Trecolori, on 47th, b/t B'way & 8th.
If you'd like to go more upscale, dbBistro Moderne, on 44th, b/t 5th & 6th, is 4-star chef Daniel Boulud's restaurant serving his take on contemporary French bistro cuisine. Delicious, of course!