How to reproduce a sound on collision?

This shows how to play a sound, and how to change the sound that is being played: http://docs.unity3d.com/Documentation/ScriptReference/AudioSource-clip.html

You'll want something like this:

 function OnCollisionEnter (collision: Collision) {
      collision.gameObject.audio.Play();
 }

That will make the object you collided with play the specified sound.