Before 1970: Metropolis (1927)
First saw this one in film class back in college and loved the imagery and story. It's stayed in my head ever since. I'd like to see it again now that there's a new restored version out.
Post 1970: Joyeux Noel (2005)
This film was recommended by a live journal friend, and I'm so glad I opted to pick it up. WWI movie, but finally one that wasn't thoroughly depressing where every character I loved died. It's a very powerful and beautiful film, depicting hope for humanity against the backdrop of one of the most terrible wars. I simply loved it.