Hello, Dolly; Singing in the Rain; Victor/Victoria - and the list could go on. I think these, and a few others like them, capture my attention with the dialogue as well as wonderful music/lyrics/color. You have to pay attention to all parts of the film, not just the "singing parts".
Also like to watch 1776 on the 4th of July (as another member mentioned), and Meet Me in St Louis always provides a new moment to say "I don't remember that from last time!" or "Run, Tootie, run!". ?