Nicolas Bouliane

Displays a custom message on the dashboard with full HTML/PHP/JavaScript support. Useful for administrator who have clients as users.
The plugin will display anything that’s in the message.php file in the plugin’s directory. Since the plugin uses a simple include, 
any kind of content is supported.

Dashboard Message

Displays a custom message on the dashboard with full HTML/PHP/JavaScript support. Useful for administrator who have clients as users.

genkisan

<ul>
<li>easily switch on and off through Admin Options</li>
<li>display message without editing theme files (above 1st post or through widget)</li>
<li>display different message to different roles/users</li>
</ul>
Demo: 
<a href="http://ericulous.com/2007/03/09/genki_announcement/" rel="nofollow ugc">Plugin Details & Demo</a>

Dashboard Message vs Genki Announcement