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>

Genki Announcement

fearnowrath

This is a very simple and straightforward plugin. The Manage/View Your Posts Only plugin is specially designed for those who have many authors or allow guest posts on their blogs. On WordPress, a contributor can write and submit a post and wait for review until it has been published. But while doing so, when they visit the “Posts” section, that lists all the posts, they are able to see posts by other contributors as well that are under review. While there may be no problem with that if all the authors are closely associated to the website or the company. However, if there are many guest writers contributing to a blog, many webmasters and site owners may not want every one of them view what others are posting and what posts are under review.
The manage your posts plugin is a simple plugin that works out of the box. Simply install the plugin and you’re ready to roll. Once the plugin is installed, a contributor can only view the posts that they have submitted and cannot see what others have been submitting. The plugin also hides the total number of posts and post drafts present on the blog to the contributors.
I wrote this plugin because I wanted this same exact feature on my blog and couldn’t find any plugin that could fix it easily.
Plugin developed by <a href="http://zibeb.com/" title="Zibeb Tips and Reviews" rel="nofollow ugc">Zibeb Tips and Reviews</a>

Manage/View Your Posts Only

Allows contributors of a blog to only view and manage their posts without seeing other contributors’ posts

Genki Announcement vs Manage/View Your Posts Only