On paper, recording a song for a film soundtrack is considered the ultimate form of selling out. The music itself is literally used as promotional material for a larger product. Music money is big, but movie money is on another level (ask Ludacris, who hasn't released an album since "Fast Five"). That being said, let's remove the negative stigma generally associated with the term "selling out" and call soundtrack inclusions what they really are: a honing in on a given artist's particular skill set to create something universally appealing to an established fan base. Studios want to produce music that a film's target demographic is going to talk about. So, depending on the scope of the project, the goals of this process vary from creating smash hit singles for major pictures (pop music for pop movies) to releasing genre classics for smaller indie flicks. As long as the music gets people talking, it succeeds.

The following 20 songs represent not only some of the most accessible music created by the performers involved, but also some of the best songs in hip-hop music.