What's your favorite Black and White movie?

I feel that the newer generations really miss out on some great films just because of the stereotype associated with being old. Feel that way about musicals too, but for another discussion...

With that being said, I'm thinking Duck Soup. I'm mostly comedies. Marx Brothers verbal banter and clever usage of of word play is right up my alley. When I try to convince people to watch it/them, I tell people Ryan Reynolds is Groucho reborn.