4. 'Grease' (1978)
Grease set a precedent, and it still ranks as the highest-grossing musical film to date. With John Travolta and Olivia Newton-John leading the film in career-making roles as star-crossed high school lovers, the Fifties-set film is a feat of perfect casting, pop-leaning songs and uproarious humor that has kept it popular through multiple generations. Prior to the film version, it was a stage musical that opened on Broadway in 1972 and was recently revived for a live TV event, and included Vanessa Hudgens, Carly Rae Jepsen and Boyz II Men in pivotal roles.