Start with ‘Double Indemnity’ directed by Billy Wilder. Then go onto the following…‘The Maltese Falcon’ directed by John Hughes, ‘The Big Sleep’ directed by Howard Hawks, ‘Gilda’ directed by Charles Vidor, ‘The Big Combo’ directed by Joseph H Lewis, ‘The Lady From Shanghai’ directed by Orson Welles, ‘Detour’ directed by Edgar G Ulmer and ‘Sunset Boulevard’ also by Billy Wilder which is not usually thought of as Noir but I think it is.
Not noir but you might find the following films enjoyable. ‘The Third Man’ and ‘Odd Man Out’ directed by Carol Reed, ‘Cat People’ directed by Jacques Tourneur, ‘Mask of Satan’ directed by Mario Bava and ‘Beyond Reasonable Doubt’ directed by Fritz Lang.
