private var b : boolean;

function OnGUI() {
    b = GUILayout.Toggle(b, "A toggle button", GUI.skin.GetStyle("Button"));
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    private bool b;
    void OnGUI() {
        b = GUILayout.Toggle(b, "A toggle button", GUI.skin.GetStyle("Button"));
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    private b as bool

    def OnGUI():
        b = GUILayout.Toggle(b, 'A toggle button', GUI.skin.GetStyle('Button'))