Double Indemnity is what is considered The Godfather of film noir. It’s a fantastic film through and through thanks to a tight and suspense-filled script from Billy Wilder and Raymond Chandler and exceptional performances by MacMurray, Stanwyck and Robinson.
The Lost Weekend is another very well made movie from Billy Wilder and features the Academy Award winning performance from star Ray Milland (and took home the Oscar for picture, director and writing).
The Apartment is a great drama-romance-comedy classic excelling with the performances by Jack Lemmon (at his absolute best IMO) and Shirley MacClaine, set against the sharp script and direction from Billy Wilder.