It's hard for me to imagine why anyone would find it useful to call any of the films listed below films noirs, but people have:
Contraband
Casablanca
To Have and Have Not
Notorious
Macao
I'll Get You
The Man From Cairo
They Were So Young
Mr. Arkadin (Confidential Report)
These are all thrillers involving romance and international intrigue, where the occasional disorientation and jeopardy of the protagonists results from being embroiled in a foreign locale, fighting a foreign system. The whole crux of the film noir tradition is that the disorientation and jeopardy take place on familiar soil, within familiar systems that have somehow grown alien, bewildering and malevolent. Night and the City is by contrast a true film noir, even though it happens to be set in London. It unfolds in a world its American protagonist knows well (though perhaps not well enough) -- his jeopardy and his doom have nothing to do with the fact that his surroundings are foreign.
Rick in Casablanca masquerades as a cynical, even nihilistic anti-hero who believes in nothing -- which gives him at least a superficial link with some film noir protagonists -- but he proves himself to be a knight in shining armor, willing to sacrifice the most important thing in his life for transcendent ideals. If this is film noir, what the hell do you call Gun Crazy or Detour -- or Night and the City, for that matter? Film noir noir?
I guess Macao gets labeled a film noir because it stars film noir icon Robert Mitchum and was made right after His Kind Of Woman, which also paired him with Jane Russell and which is an actual film noir, or at the very least a comic parody of one. The rest are mostly standard spy thrillers involving an innocent American caught in a web of foreign intrigue.
I think you could make a case that John Le Carré's existentially bleak spy thrillers enter the realm of noir, or neo-noir, but the romantic adventures and thrillers above don't come close.
[The noir credentials of the films listed above are as follows . . . Contraband is included in a film noir DVD box set from Kino . . . Casablanca, Notorious and To Have and Have Not are listed on the Wikipedia "expanded list" of classic films noirs . . . Macao is among the films noirs listed in Nicholas Christopher's Somewhere In the Night . . . I'll Get You, The Man From Cairo and They Were So Young are included in the VCI series Forgotten Noir.]