"It's straight down the line for both of us. Remember!" - Double Indemnity

I love this. It is the ultimate film noir dialog and in a way it sums up all of film noir
"Yeah, I remembered it all right. Just as I remembered what you had told me, Keyes, about that trolley car ride, and how there was no way to get off until the end of the line, where the cemetery was. And I got to thinking what cemeteries are for. They're to put dead people in..."