Rotation Script

gistfile1.cs

using UnityEngine;
using System.Collections;

public class RotateObject : MonoBehaviour {

    public float RotationPerPixelMovement = 1.0f;

    GameObject _toRotate;
    bool _rotating = false;
    Vector3 _lastPosition;
    Vector3 _objEulerAngles;

    void Update()
    {
        CheckForActivation();
        HandleRotation();
    }

    void CheckForActivation()
    {
        if (Input.GetMouseButtonDown(0) && FindObjectUnderCursor())
        {
            _lastPosition = Input.mousePosition;
            _objEulerAngles = _toRotate.transform.rotation.eulerAngles;
            _rotating = true;
        }
        else if (Input.GetMouseButtonUp(0))
        {
            _rotating = false;
        }
    }

    bool FindObjectUnderCursor()
    {
        var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        RaycastHit rh;
        if (Physics.Raycast(ray, out rh, float.MaxValue))
        {
            _toRotate = rh.collider.gameObject;
            return true;
        }
        return false;
    }

    void HandleRotation()
    {
        if(!_rotating) 
        {
            return;
        }

        var pos = Input.mousePosition;
        var delta = pos - _lastPosition;
        _lastPosition = pos;
        _objEulerAngles.x += delta.y * RotationPerPixelMovement;
        _objEulerAngles.y -= delta.x * RotationPerPixelMovement;
        _toRotate.transform.rotation = Quaternion.Euler(_objEulerAngles);
    }
}