MonoBehaviourUtility for shared instances. The beauty of Singletons.

ExampleManager.cs

using UnityEngine;
using System.Collections;

public class ExampleManager : MonoBehaviour 
{   
    static public ExampleManager sharedManager 
    {
        get 
        {
            return MonoBehaviourUtility.GetManager<ExampleManager>( ref _sharedManager );
        }
    }   
    static private ExampleManager _sharedManager;       
}

MonoBehaviourUtility.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.IO;

static public class MonoBehaviourUtility
{

    static public T GetManager<T>( ref T manager ) where T : MonoBehaviour
    {
        if (manager == null)
        {
            manager = (T)GameObject.FindObjectOfType( typeof( T ) );
            if (manager == null)
            {
                GameObject gameObject = new GameObject( typeof( T ).ToString() );
                manager = (T)gameObject.AddComponent( typeof( T ) );
            }
        }
        return manager;
    }

}