Here is a great dynamic countdown clock made in java script:

You can customize the background color, foreground color, target date, and messages.

Here is the code:
<p align="center"> <script language="JavaScript"><br />TargetDate = "12/31/2020 5:00 AM";<br />BackColor = "black";<br />ForeColor ="green";<br />CountActive = true;<br />CountStepper = -1;<br />LeadingZero = true;<br />DisplayFormat = "%%D%% Days, %%H%% Hours, %%M%% Minutes, %%S%% Seconds.";<br />FinishMessage = "It is finally here!";<br /></script><script language="JavaScript" src="http://evolution.wapath.com/js/countdown.js"></script> <br /> </p>