I'm up, I'm up.
Vertigo is, of course, obvious in today's topic o' the day. Critics didn't like it, and audiences stayed away, and today most folks consider it a masterpiece.
I also find it happens with certain musical films, but for a much smaller percentage of fans - things like Half a Sixpence and Darling Lili and Hello, Dolly, and even Man of La Mancha - to read comments on the imdb, you'd think these films were masterpieces, too.