The Wizard Of Oz
If you don't know this movie without being told about it, I don't want to know you.
While mediocre in original release, barely breaking even for its $2.7M budget, it was properly recognized by being one of the ten films nominated for Best Picture in 1939 (five of which continue to shine, and three of which make my list here). Won two Oscars for music, including Best Original Song for "Somewhere Over The Rainbow", timelessly and flawlessly sung by Louis B. Mayer's third choice for her role, a young studio protégé suddenly known for all time worldwide as Judy Garland, then all of sixteen years of age. It was once classified as a "cult favorite", until television ratings and DVD/BD sales indicated that would require "cult" to be re-defined as "nearly every living American born after 1930". It is now consistently rated at one of the Top Ten Movies Of All Time on list after list, and has passed beyond mere film to a touchstone of American culture, and rightly so.