This is so not my forté. I just don't watch any movies that are purely romance. There are plenty with romance subplots, though, so I'm going to count those and so will you.
For the sake of familiarity I'm going to exclude any anime nominations (where the winners are 5 Centimeters Per Second, Lupin III: Castle of Cagliostro, and The Girl Who Leapt Through Time) in favor of titles y'all may have heard of.
Like Beauty and the Beast. Or Somewhere in Time. Or The Sound of Music. Or Airplane!. Because they're what I'd nominate. And if you haven't seen any of them, then shame on you.