FirstPersonLookAt.cs

using UnityEngine;
using System.Collections;

// On first-person controllers, the camera and body are separate objects,
// so to perform a smooth look-at, they must rotate along different axes, in unison.
// NOTE: You will likely have to disable the look/camera controller in order for this to work.

public class FirstPersonLookAt : MonoBehaviour 
{
	public Transform body;
	public Transform camera;
	public Transform target;
	public float speed = 5f;
	public Vector3 offset;
	public bool follow;

	void Update () 
	{
		if (target != null)
		{
			// rotate body around y-axis
			Vector3 direction = (target.position + offset) - body.position;
			direction.y = 0; // forces rotation around y-axis
			Quaternion bodyRotation = Quaternion.LookRotation(direction);
			body.rotation = Quaternion.Slerp(body.rotation, bodyRotation, speed * Time.deltaTime);

			// rotate camera around x-axis locally
			direction = (target.position + offset) - camera.position;
			Quaternion cameraRotation = Quaternion.Inverse(bodyRotation) * Quaternion.LookRotation(direction); // get difference of rotations to limit to x-axis local rotation
			camera.localRotation = Quaternion.Slerp(camera.localRotation, cameraRotation, speed * Time.deltaTime);

			// stop when target reached, unless set to follow
			if (!follow)
			{
				if (Quaternion.Angle(camera.localRotation, cameraRotation) < 0.1f
				    && Quaternion.Angle(body.rotation, bodyRotation) < 0.1f)
				{
					target = null; // reset target and stop
				}
			}
		}
	}
}