Of the above listed, my selection is Billy Wilder, whose masterpieces Sunset Blvd. and Some Like it Hot are among my most watched titles.
Of those not listed, I would call out George Cukor (Born Yesterday, A Star Is Born, Les Girls) and John Huston (The Quiet Man, The Searchers), as well as John Huston (The African Queen, Moby Dick) and Sidney Lumet (12 Angry Men).
Several directors got their start in the 1950s: Federico Fellini (Variety Lights), Stanley Kubrick (Fear and Desire), Ed Wood (Glen or Glenda), Delbert Mann (Marty), Charles Laughton (The Night of the Hunter), Roger Corman (Samp Woman), Stanley Kramer (Not as a Stranger), Sidney Lumet (12 Angry Men), Robert Altman (The Delinquents), Martin Ritt (Edge of the City), Jack Clayton (Room at the Top), Tony Richardson (Look Back in Anger), Alain Renais (Hiroshima, Mon Amour) and John Cassavetes (Shadows).
Cecil B. DeMille ended his legendary career in this decade, making The Ten Commandments his last masterpiece.
My favorite stand-alone films of the 1950s are as follows: Sunset Blvd., Some Like It Hot, On the Waterfront, All About Eve, A Bridge on the River Kwai, Singing’ in the Rain, High Noon, Rear Window, East of Eden, Ben-Hur, 12 Angry Men, An American in Paris.