Titanic

Anyone who was old enough to remember cannot think of "Titanic" without thinking of Celine Dion belting out "My Heart Will Go On" on the radio.   It is a classic example of a song being used to mass market a film and increase it's popularity.  The film's iconic score can also be heard instrumentally at several parts throughout the film.  For example, during the scene where Rose and Jack are at the bow of the boat, "Flying".  Also, the song can be heard instrumentally when an adult Rose drops her necklace in the ocean at the film's climax.

Other than "My Heart Will Go On", music plays a huge role within the film.  The music, beginning with Rose's flashback, is light and characterized by an almost humming sound.  The human sounding whispers convey that Rose's memory is akin to a whisper from the past.  The music becomes more vivid and intense at times when strong emotion is conveyed; for example, excitement when Jack watches the Dolphins jump alongside the ship, or fear when Rose wades through the sinking ship to rescue Jack from the Master of Arms.

In addition to conveying emotion, music in "Titanic" also serves to establish time and place.  It also serves to highlight the contrast between the passengers in first class and those in steerage.  When Rose is in the company of her mother and their group, the music is soft chamber music, waltzes, mostly played by string quartet, which incidentally plays a large role later in the film.  In contrast, during the party below deck, the music is loud, with foreign instruments to convey that the people listening are not of one nationality.  Also the instruments heard are less "traditional" than those in the string quartet; things like fiddles, bag pipes, and drums.  

Diegtic music plays a large part in "Titanic."  The earlier mentioned String Quartet serves as a powerful and emotional reminder of the power of music when they play together even as the boat continues to sink.  Another interesting little quirk of the music in "Titanic" is the little song, "come see Josephine in her flying machine..." which Jack sings to Rose during the height of their love affair, and which Rose sings to herself, as she clutches to life and freezes on the floating door.  

The music within "Titanic" is both powerful and poignant, and it serves the purpose of conveying emotion as well establishing time and place.