Any thoughts on a "must not miss" restaurant for lunch in Manhattan in December? Thank you!

Cafe Sabarsky in the NeueGallerie?

Give us some more to go on. What neighborhood? What kind of cuisine? What's your price range?

There are hundreds of them!
3 questions:
What area of the city? What type(s) of food? What price range?

Well two that come to mind are having lunch at Le Bernadin and having a hot dog at a stand near Rockefeller Center.

There are some great prix fixe lunch "deals." Some of the top French restaurants have them- La Cote Basque ($38), La Caravelle ($38), Le Perigord ($28), Cafe Boulud ($29). People have been raving lately about Toqueville which I haven't tried yet. They have a $20.03 lunch (it's near Union Square). Aquavit also has a $20.03 lunch. I think lunch is a great time to try some of these top places. As others have said, neighborhood, ambiance & type of food would help to steer you.