Add editor buttons to your MonoBehaviours methods

BehaviourButtonsEditor

using UnityEditor;
using UnityEngine;

namespace BitStrap
{
	/// <summary>
	/// Custom editor for all MonoBehaviour scripts in order to draw buttons for all button attributes (<see cref="ButtonAttribute"/>).
	/// </summary>
	[CustomEditor( typeof( MonoBehaviour ), true, isFallback = true )]
	[CanEditMultipleObjects]
	public class BehaviourButtonsEditor : Editor
	{
		private ButtonAttributeHelper helper = new ButtonAttributeHelper();

		public override void OnInspectorGUI()
		{
			base.OnInspectorGUI();
			helper.DrawButtons();
		}

		private void OnEnable()
		{
			helper.Init( target );
		}
	}
}

ButtonAttribute

namespace BitStrap
{
	/// <summary>
	/// Put this attribute above one of your MonoBehaviour method and it will draw
	/// a button in the inspector automatically.
	///
	/// NOTE: the method must not have any params and can not be static.
	///
	/// <code>
	/// <para>[Button]</para>
	/// <para>public void MyMethod()</para>
	/// <para>{</para>
	/// <para>    Debug.Log( "HELLO HELLO HELLO!!" );</para>
	/// <para>}</para>
	/// </code>
	/// </summary>
	[System.AttributeUsage( System.AttributeTargets.Method )]
	public class ButtonAttribute : System.Attribute
	{
	}
}

ButtonAttributeHelper

using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using UnityEditor;
using UnityEngine;

namespace BitStrap
{
    /// <summary>
    /// Searches through a target class in order to find all button attributes (<see cref="ButtonAttribute"/>).
    /// </summary>
    public class ButtonAttributeHelper
    {
        private static object[] emptyParamList = new object[0];

        private IList<MethodInfo> methods = new List<MethodInfo>();
        private Object targetObject;

        public void Init(Object targetObject)
        {
            this.targetObject = targetObject;
            methods =
                targetObject.GetType()
                    .GetMethods(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                    .Where(m =>
                            m.GetCustomAttributes(typeof(ButtonAttribute), false).Length == 1 &&
                            m.GetParameters().Length == 0 &&
                            !m.ContainsGenericParameters
                    ).ToList();
        }

        public void DrawButtons()
        {
            if (methods.Count > 0)
            {
                EditorGUILayout.HelpBox("Click to execute methods!", MessageType.None);
                ShowMethodButtons();
            }
        }

        private void ShowMethodButtons()
        {
            foreach (MethodInfo method in methods)
            {
                string buttonText = ObjectNames.NicifyVariableName(method.Name);
                if (GUILayout.Button(buttonText))
                {
                    method.Invoke(targetObject, emptyParamList);
                }
            }
        }
    }
}