Example code for "Building a menu of delegates and enums" blog post on AngryAnt.com

Menu.cs

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

public class Menu : MonoBehaviour
{
	delegate void OnGUIImplementation();
	public enum MenuState {Main,Settings,Credits};
	public struct Settings
	{
		public bool m_ThisSetting, m_ThatSetting, m_TheOtherSetting;
	};
	static Vector2 m_StandardMenuSize = new Vector2 (200.0f, 300.0f);
	static string m_LogoURL = "http://download.unity3d.com/images/top-menu/mm_unity_icon.png";
	static Texture2D m_Logo = null;

	private MenuState m_CurrentState = MenuState.Main;
	private Dictionary m_Menus;
	private Settings m_Settings;



	void Awake ()
	{
		m_Menus = new Dictionary ();
		m_Menus [MenuState.Main] = OnMainMenuGUI;
		m_Menus [MenuState.Settings] = OnSettingsGUI;
		m_Menus [MenuState.Credits] = OnCreditsGUI;
		StartCoroutine (GetLogo ());
	}



	IEnumerator GetLogo ()
	{
		WWW www = new WWW (m_LogoURL);

		yield return www;

		if (www.error == null)
		{
			m_Logo = www.texture;
		}
	}



	public void OnGUI ()
	{
		m_Menus [m_CurrentState] ();
	}



	static void BeginStandardMenu (string title)
	{
		GUILayout.BeginArea (new Rect ((Screen.width - m_StandardMenuSize.x) * 0.5f, (Screen.height - m_StandardMenuSize.y) * 0.5f, m_StandardMenuSize.x, m_StandardMenuSize.y));
			GUILayout.BeginVertical (GUI.skin.GetStyle ("Box"));
				GUILayout.Label (title, GUI.skin.GetStyle ("Box"));
	}



	static void EndStandardMenu ()
	{
		Color color;

				GUILayout.BeginHorizontal ();
					GUILayout.FlexibleSpace ();
						color = GUI.color;
						GUI.color = Color.grey;
						GUILayout.Label ("My game version 2.4X");
						GUI.color = color;
					GUILayout.FlexibleSpace ();
				GUILayout.EndHorizontal ();
			GUILayout.EndVertical ();
		GUILayout.EndArea ();
	}



	void OnMainMenuGUI ()
	{
		BeginStandardMenu ("Main menu");
			if (m_Logo != null)
			{
				GUILayout.BeginHorizontal ();
					GUILayout.FlexibleSpace ();
						GUILayout.Label (m_Logo);
					GUILayout.FlexibleSpace ();
				GUILayout.EndHorizontal ();
			}
			if (GUILayout.Button ("New game"))
			{
				Application.LoadLevel ("Level one");
			}
			m_CurrentState = GUILayout.Button ("Settings") ? MenuState.Settings : m_CurrentState;
			m_CurrentState = GUILayout.Button ("Credits") ? MenuState.Credits : m_CurrentState;
			GUILayout.FlexibleSpace ();
		EndStandardMenu ();
	}



	void OnSettingsGUI ()
	{
		BeginStandardMenu ("Settings");
			m_Settings.m_ThisSetting = GUILayout.Toggle (m_Settings.m_ThisSetting, "This setting");
			m_Settings.m_ThatSetting = GUILayout.Toggle (m_Settings.m_ThatSetting, "That setting");
			m_Settings.m_TheOtherSetting = GUILayout.Toggle (m_Settings.m_TheOtherSetting, "The other setting", GUI.skin.GetStyle ("Button"));
			GUILayout.FlexibleSpace ();
			m_CurrentState = GUILayout.Button ("Main menu") ? MenuState.Main : m_CurrentState;
		EndStandardMenu ();
	}



	void OnCreditsGUI ()
	{
		BeginStandardMenu ("Credits");
			GUILayout.Label ("This game was created by some of the most awesomestest people on the planet. Having failed in their mission to Pluto, they started making games, which - as you can see - resulted in much joy and success!");
				GUILayout.Space (20.0f);
				GUILayout.BeginHorizontal ();
					GUILayout.FlexibleSpace ();
						GUILayout.Label ("The awesomestest people inc.");
				GUILayout.EndHorizontal ();


			GUILayout.FlexibleSpace ();
			m_CurrentState = GUILayout.Button ("Main menu") ? MenuState.Main : m_CurrentState;
		EndStandardMenu ();
	}
}

NewSubmenu.cs

m_Menus [MenuState.MyMenuState] = OnMyMenuGUI;

OnGUI.cs

public void OnGUI ()
{
	m_Menus [m_CurrentState] ();
}

SwitchMenu.cs

m_CurrentState = GUILayout.Button ("Credits") ? MenuState.Credits : m_CurrentState;

Can you update this to work with unity 4?