Monsters Inc Introduction

A good example of using animation to represent sound is the intro to the film Monsters Inc:



The doors open/close and move to the music, which gives the illusion that the animation is running smoother, since every aspect of this piece combines together to complete the sequence.

Especially the sequence at 0.44 when the door becomes a saxophone to produce the letters; it's an interesting and imaginative way to animate the doors, which keeps the viewers interested in the film.