iTween Rotate and Look at the Object.

Or you could use iTween's LookUpdate() which would introduce easing and has more options available ():

var LookAtTarget : Transform;

 function Update ()
 {
     LookUpdate(gameObject, LookAtTarget.position, 2);
 }

You can learn more from the documentation.

Would you like the camera to keep rotating? if so in wat direction?

and to make the camera face an object you would use this code

var camera : Tranform; //select your camera for this one

var LookAtTarget : Transform;

 function Update ()
 {
     transform.LookAt(LookAtTarget);
 }

This should work. :)

I would like to make the camera rotate in round shape while it keep looking at the gameObject.

Please help. Thanks.

I have used

var rotation = Quaternion.Euler(40, velocity, 0);       
    var position = rotation * Vector3(0, 0.8, -6.8)+target.position;
    transform.rotation = rotation;
    transform.position = position;

but it is pain because when I start to run the game, the camera is "stuttered" at the beginning and runs smooth after that, so I'm trying to use iTween to solve this problem.

Any suggestion?