Mdkart

The countdown can works in two ways : for futur and past events : until the events (in 43 days for example) and since the events (for 96 days)
So this plugin is very interesting for major (or minor) events of the life, birthdays, etc…
<h4>Feature List</h4>
<ul>
<li>Unlimited DDays stocked in the database</li>
<li>Function of repetition of the Dday. For example : every year for birthday.</li>
<li>Posibility to give a title, an URL, a description…</li>
<li>Customizable format of display (ex : The balise %TITLE% will be replaced by the title of the DDay). This allows a simply translation in any language.</li>
<li>Advanced interface of management of the DDays : selection of the order by drag and drop, realtime form validation.</li>
<li>Posibility to insert the list of the DDays in the sidebar or to insert a specific DDay in a post</li>
</ul>

DDay

This plugin allow to associate a countdown to events.

Michael Henke

This plugin will display a count down in days until a certain date. 
This date can be set in the wordpress administration panel as well as the text related to it.
For example:
<ul>
<li>Our wedding will be in 14 days.</li>
<li>31 days until final exams.</li>
<li>In 2 days Apple will release its iPad…</li>
</ul>
The plugin can be used in a widgetized sidebar or in your theme.
On the configuration panel is also a donation link, so you can chip in to my own wedding budget if you like. 
The upcoming wedding of my fiancée and me was the inital reason of writing this plugin. 
You can read about our wedding and preparations at <a href="http://www.hasenha.us/" title="Willkommen im Hasenha.us!" rel="nofollow ugc">hasenha.us</a> 
and of course you can see the plugin in action there.

Simple Count Down

Simple configurable widgetized count down plugin.

DDay vs Simple Count Down