Editor extension that adds a tool to automagically generate boilerplate custom inspector code~ YES! Just drop it into a folder called 'Editor' and it adds a 'custom inspector' option into the Project window!

CustomInspectorCreator.cs

using UnityEngine;
using UnityEditor;
using System.IO;

public static class CustomInspectorCreator
{
    [MenuItem("Assets/Create/Custom Inspector", priority = 81)]
    static void CreateInsptorEditorClass()
    {
        foreach (var script in Selection.objects)
        {
            BuildEditorFile(script);
        }
        
        AssetDatabase.Refresh();
    }

    [MenuItem("Assets/Create/Custom Inspector", priority = 81, validate = true)]
    static bool ValidateCreateInsptorEditorClass()
    {
        foreach (var script in Selection.objects)
        {
            string path = AssetDatabase.GetAssetPath(script);

            if (script.GetType() != typeof(MonoScript))
                return false;
            if (!path.EndsWith(".cs"))
                return false;
            if (path.Contains("Editor"))
                return false;
        }

        return true;
    }

    static void BuildEditorFile(Object obj)
    {
        MonoScript monoScript = obj as MonoScript;
        if (monoScript == null)
        {
            Debug.Log("ERROR: Cannot generate a custom inspector, Selected script was not a MonoBehavior");
            return;
        }

        string assetPath = AssetDatabase.GetAssetPath(obj);
        var filename = Path.GetFileNameWithoutExtension(assetPath);
        string script = "";
        string scriptNamespace = monoScript.GetClass().Namespace;

        if (scriptNamespace == null)
        {
            // No namespace, use the default template
            script = string.Format(template, filename);
        }
        else
        {
            script = string.Format(namespaceTemplate, filename, scriptNamespace);
        }
        
        // make sure a editor folder exists for us to put this script into...       
        var editorFolder = Path.GetDirectoryName(assetPath) + "/Editor";

        if (!Directory.Exists(editorFolder))
        {
            Directory.CreateDirectory(editorFolder);
        }

        if (File.Exists(editorFolder + "/" + filename + "Inspector.cs"))
        {
            Debug.Log("ERROR: " +filename + "Inspector.cs already exists.");
            return;
        }

        // finally write out the new editor~
        File.WriteAllText(editorFolder + "/" + filename + "Inspector.cs", script);
    }

    #region Templates
    static readonly string template = @"using UnityEngine;
using UnityEditor;
using System.Collections;
using System.Collections.Generic;

[CustomEditor(typeof({0}))]
//[CanEditMultipleObjects]
public class {0}Inspector : Editor
{{
    void OnEnable()
    {{
        // TODO: find properties we want to work with
        //serializedObject.FindProperty();
    }}

    public override void OnInspectorGUI()
    {{
        // Update the serializedProperty - always do this in the beginning of OnInspectorGUI.
        serializedObject.Update();

        // TODO: Draw UI here
        //EditorGUILayout.PropertyField();
        DrawDefaultInspector();

        // Apply changes to the serializedProperty - always do this in the end of OnInspectorGUI.
        serializedObject.ApplyModifiedProperties();
    }}
}}
";

    static readonly string namespaceTemplate = @"using UnityEngine;
using UnityEditor;
using System.Collections;
using System.Collections.Generic;

namespace {1}
{{
    [CustomEditor(typeof({0}))]
    //[CanEditMultipleObjects]
    public class {0}Inspector : Editor
    {{
        void OnEnable()
        {{
            // TODO: find properties we want to work with
            //serializedObject.FindProperty();
        }}

        public override void OnInspectorGUI()
        {{
            // Update the serializedProperty - always do this in the beginning of OnInspectorGUI.
            serializedObject.Update();

            // TODO: Draw UI here
            //EditorGUILayout.PropertyField();
            DrawDefaultInspector();

            // Apply changes to the serializedProperty - always do this in the end of OnInspectorGUI.
            serializedObject.ApplyModifiedProperties();
        }}
    }}
}}
";
    #endregion
}

example.png

ValidateCreateInsptorEditorClass() needs a check for when nothing is selected (ie, Selection.objects.Length == 0).
Otherwise, line 30 throws an IndexOutOfRangeException whenever you just right-click on the Project panel.

Other than that, I love it! And nice code form too. Very readable and self-documenting. Thanks for sharing it!
I was meaning to write this editor script for myself but I always kept putting it off.

@pharan ahh thanks for the report!! ♥ I had already updated the gist just before i saw that comment to support multiple file selections, that change cleaned up ValidateCreateInsptorEditorClass() and should also totally fix that exception too. worth an upgrade :3