Slowing rotation to a stop using Time.time

Hi all. I hope I have a easily solved scripting problem but it's a bit beyond my limited scripting talents right now. I just want to use a time function to slow an objects rotation to a stop.

Basically the object has a variable rotation that needs to be slowing over time. When it hits a certain low rotational threshold I want it to stop or in a future iteration call an animation that will make the object fall over and "die."

Here's what I have so far and a big thanks to anyone who can help me out.

//start rotate speed

var rotateStart = 300;

function Update ()

{

if (rotateStart >=30)

{

transform.Rotate (0,0,(rotateStart/(300*Time.time)));

}

else

{

transform.Rotate (0,0,0);

}

}