No list of romantic films is complete without Eric Rohmer (The Green Ray, My Girlfriend's Boyfriend..)- fresh, young , spontaneous and summery-, and Max Ophuls (Letter from an Unknown Woman, Liebelei)- exquisite Viennese period confections.

i'll second; Sunrise (wonderful), L'Atalante, In the Mood for Love. 

Also; Lovers of the Arctic Circle (terribly touching), Ai no Corrida (love as sado-masochistic sex), Show me Love (teenage lesbian love).   

The most romantic moment in cinema is the end of The Green Ray. 