There are many films where the film becomes a massive success because of its music. Examples being -
Love Story (1981)- earned 5.75 crores, Golden Jubilee Hit, Blockbuster. Became one of the best debut for an actor with Kumar Gaurav becoming an instant star.
Bettaab (1983)- earned 6.75 crores, Blockbuster Hit. Sunny Deol became an instant star with the film. Directed by the same Rahul Rawail who directed Love Story.
Hero (1983)- 6.25 crores, Blockbuster Hit. Launched the careers of Jackie Shroff and Meenakshi Seshadri in bollywood
Pyar Jhukta Nahi (1985)- a film which was delayed by 2 years, no distributor was ready to buy the film, music released by a new company called T Series, became such a big musical success that the film ended up becoming a blockbuster Hit with a collection of 4.50 crores
Lal Dupatta Malmal ka (1988)- the film was originally conceived only as an album but the album became such a big hit that they made a film for it and released it directly on casettes. Sold more than 1 lakh video casettes.
Aashiqi (1990)- Again this was conceived as an album but Mahesh Bhatt asked T series to give him the songs for a movie. Result was an extraordinary album which sold more than 2 crores copies. The film was also a massive success with a collection of 4 crores. It was followed by series of such musicals like Sajan (1991), Deewana (1992), Dil hai ki Manta Nahi (1991) etc
Rang (1993)- The last film of Divya Bharti, the last hit of Jeetendra and the only hit of Kamal Sadanah. Reason- beautiful music on the basis of which the film got success.
The second category of films is where the music becomes popular but not the film. So you know the song very well but not the film.
Chalte Chalte (1976): Nobody remembers this film or its hero Vishal Anand but the music was a chartbuster including songs like Pyar me Kabhi Kabhi Aisa ho jaata hai and Chalte chalte mere ye Geet yaad rakhna etc. People listen to these songs but don't know the film.
Waisa bhi Hota hai Part 2 (2003)- There is no part 1 both parts are in the same film. This is a film which is only known for its music and it has two very popular songs even though I bet hardly anyone knows that the songs are from this film. The music was composed by Vishal Shekhar. The first good song is “Sajna Aa bhi Jaa” a romantic song that became popular. And the second song is very very popular. It is called “Allah ke Bande Hans de” sung by Kailash Kher. Many people think that this song is from Kailash kher’s album but the song is in this film and Kailash Kher also features in the film.