You might not be one of those people who really notice the music in movies. Most of us aren't, actually. A lot of the time, it's designed that way; they want the music to help set the scene, so if it really fits, you might not notice it at all.

However, there are a few examples of moments where the music just grabs you. Think about Jaws. Think about Amelie.

Like those films, the Star Wars flicks have some of the most iconic themes in American history. Written by John Williams (yes, the John Williams, also responsible for the music behind Jaws, among many other movies), and performed by the London Symphony Orchestra, the sound of all of the Star Wars movies is orchestral and grand and intensely moving.

The most famous composition from the series is probably "The Imperial March": the bum bum bummm, bum, bah-bum, bum, bah-bummmm that accompanies Darth Vader whenever he walks into a room. (If you can't hear it in your head right now, you're going to kick yourself because you know this theme.)

But, all of the music in these films are iconic—and it all means something. Williams felt that his role was to establish themes for the main characters and places so that the music could summon up a place or person as well as their image could. When those characters clashed, he would meld their respective melodies together in an impressive upswell of familiar note phrasing and embellishments. The guy really is a genius.

Revenge of the Sith, however, marks a slight departure from this tendency. For this movie, he admitted that he wanted a less obvious underscore to help support its darker nature. (Source)

He also wanted to utilize his old scores from the original trilogy in new ways instead of inventing completely new songs in order to help create a bridge between the prequels and the more familiar classics. So, instead of a new villain theme for the budding Darth Vader, we catch whiffs of "The Imperial March" as Anakin descends deeper into the dark side.

And, in a moment of uncontainable nostalgia, we get the familiar music for Luke's home planet of Tatooine at the very end, building a perfect conduit to carry us over into Episode IV.