Script for making player face the direction of the mouse cursor.

gistfile1.cs

using UnityEngine;
using System.Collections;
 
public class LookAtMouse : MonoBehaviour {
 
	// speed is the rate at which the object will rotate
	public float speed;
	
	void FixedUpdate () {
	
	    // Generate a plane that intersects the transform's position with an upwards normal.
	    Plane playerPlane = new Plane(Vector3.up, transform.position);
	
	    // Generate a ray from the cursor position
	    Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
	
	    // Determine the point where the cursor ray intersects the plane.
	    // This will be the point that the object must look towards to be looking at the mouse.
	    // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
	    // then find the point along that ray that meets that distance.  This will be the point
	    // to look at.
	    float hitdist = 0.0f;
	    
	    // If the ray is parallel to the plane, Raycast will return false.
	    if (playerPlane.Raycast (ray, out hitdist)) {
	    
		    // Get the point along the ray that hits the calculated distance.
		    Vector3 targetPoint = ray.GetPoint(hitdist);
		
		    // Determine the target rotation.  This is the rotation if the transform looks at the target point.
		    Quaternion targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
		
		    // Smoothly rotate towards the target point.
		    transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
		}
    }
}