Remi Corson

This plugin helps admins to easily create admin notification inside the WordPress administration.
You can choose many options and decide how and where to display the notifications.

Easy Admin Notification

Tested up to 3.3.1 Stable Tag: 1.4 Adds the ability to create easily notification in the admin panel

freemp

A simple, lightweight WordPress plugin for displaying a notification bar at the top of the webpage if 1st-party JavaScript is disabled. If appropriate, the entire website may as well be blocked by a full-page overlay instead of just a small bar.
The plugin offers configuration of background and foreground color, opacity, notification message text and font size. Individual customization by means of CSS snippets is also supported.

JavaScript Notifier

JavaScript Notifier allows you to inform visitors that your website requires JavaScript.

Easy Admin Notification vs JavaScript Notifier