Black Swan and the awful dream sequence in Oklahoma! The film is on a number of "Best" lists, including the 501 Must See Movies, imdb's top 250 bubbling under, and filesite lists top 100. A British film that I at least had the pleasure of watching in high definition in a spiffy remastering that recently came out.
The film is more of a fantasy ballet than a musical. The leading character's don't sing, but perform. I'm starting to realize that the musical genre encapsulates a number of "stage performance" films that aren't really musicals at all. The film centers around the redheaded Moira Shearer who plays Victoria Page, a young prima ballerina, who is under strict guidance of the company manager.
The performance of "The Red Shoes" ballet is very odd. Blurring the line between reality and fantasy the "stage" performance is impossible with a constantly changing scenery and bizarre direction. At first all I could think was "how the hell is this a possible performance?" I didn't get it, didn't like the characters, or the movie in general. Don't watch this one.
IMDB Link: http://www.imdb.com/title/tt0040725/