"Roads ...? Where we're going we don't need roads !"  Doc

I love the Hitchcock ones.  Check out Vertigo, Man Who Knew Too Much, Dial M For Murder, To Catch A Thief, etc.

Hitchcock's movies are fantastic (of course not all of them!). "Strangers on a train", "Vertigo" and "Rear Window" are my favourite ones (James Stewart is such a great actor).
Since you like Audrey Hepburn, I recommend you "Charade" of Stanley Donen with the marvelous Cary Grant. Talking about M. Grant, he also played in "Monkey Business" with Marilyn Monroe, this movie was not really interesting but still a nice comedy to watch. Another mythical actress : Bette Davis, in my opinion this woman has class. I loved her in "All about Eve" by Mankievicz.
I love all Chaplin's movies, M. Verdoux is not well known but really interesting. "Freaks" of Tod Browning is a movie you have to watch. Of course "King-Kong" (the first version, of Cooper and Schoedsack).

I could recommand you some old french movies : "The River" (Jean Renoir); "The Beauty and the Beast" (Jean Cocteau) which is really poetic; if you like the New Wave and Brigitte Bardot, you should watch "Et Dieu... créa la Femme" (Roger Vadim).

Ok, I have to stop now. Hope you'll find at least one movie that you like.