SINGIN' IN THE RAIN, 1952

Director: Stranley Donen and Gene Kelly 
Writers: Adolph Green and Betty Comden 
Stars: Gene Kelly, Donald O'Connor and Debbie Reynolds 
Plot: In 1927, Don Lockwood and Lina Lamont are a famous on-screen romantic pair. Lina, however, mistakes the on-screen romance for real love. Don has worked hard to get where he is today, with his former partner Cosmo. When Don and Lina's latest film is transformed into a musical, Don has the perfect voice for the songs. But Lina - well, even with the best efforts of a diction coach, they still decide to dub over her voice. Kathy Selden is brought in, an aspiring actress, and while she is working on the movie, Don falls in love with her. Will Kathy continue to "aspire", or will she get the break she deserves?

Singin' in the rain trailer 

Recommendations: Here you have some other musicals: Seven Brides for Seven Brothers, 1954, All That Jazz, 1979 and West Side Story, 1961.
Singin' in the rain is probably the best musical of ever.