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!

andy

This Plugin allows you to display time and date from all timezones. The setup page generates the shortcode you like. Just copy & paste this code on every place you want. The time is adjusted to the server time. 
Formats: 
 * Time (without seconds) 
 * Time 
 * Date (local format) 
 * Date 
 * Daten and Time

Saan World Clock

This Plugin display date and time of all timezones (Server time adjusted). Easy to use with shortcodes.

WP Coming Soon vs Saan World Clock