Just one? My top 5 (not necessarily in order) list includes:

-My Fair Lady (or Pretty Woman, but the one being a musical makes it better); just a feel good story, and the number of pop-culture references to it
-Rent; because we need to learn to appreciate the time we have
-Medicine Man; cause our own progress shall be our undoing
-Contact; cause we really don't know what's out there
-Memoirs of a Geisha; cause a little insight into another's world is a good thing