I mean, okay, I liked the Maltese Falcon, but yr probly gna say that's a cop-out answer.
Double Indemnity is pretty much the one that started it all, so, that's a good place to start.
They Live By Night is good, too. When you watch that one, you must keep in mind that "teenager" is a concept that literally did not exist yet, at that point in time. Wasn't a thing at all. You were a kid, then bam! adulthood. Gives the kid in a tie and a leather jacket a whole new dimension.
And, The Killers. Because Kitty is fuckin' hot. The way she rocks that dress, and is so nonchalant about it? Work it girl.