Miriam de Paula

WP Coming Soon is a plugin that adds a countdown clock in the Coming Soon page. This plugin uses Keith Wood jQuery plugin. See it at: http://keith-wood.name/countdown.html.
[BASIC USAGE]
Put this <code>if ( function_exists('get_countdown')) get_countdown();</code> where you want to display the countdown clock…
If you want to use the countdown timer within a page or page template, you can use the shortcode <code>[wp_coming_soon]</code>

WP Coming Soon

WP Coming Soon is a simple plugin that adds a countdown clock in your Coming Soon page... Nothing more!

flexostudio

Countdown Clock 
see: http://www.flexostudio.com/
<h3>How to use</h3>
1.Going by the settings in the administration and data entry required to start the clock. Generate code and copy it and put the desired location and you’re done. 
or 
2. paste the following code to the desired location in the code of your page: 
example: 
 $con='[flexocounter endDate=”30.09.2011 10:30″ url=”http://google.com” header=”text” footer=”text”]’; 
 flexoCounter::the_content($con); 
$con generate in the administration too

WP Coming Soon vs Flexo Counter