PHP would be an easy way to go. All you would need to do is create the menu as you would like it in a seperate file and then include it with the PHP with the following code
Code:
<?php include 'file.txt'; ?>
You can use whatever sort of extension you want since all it does is pull the content from that file and puts it in the page that is including it, replacing the PHP code.
The server reads is and if anyone checks your source it shows the menu code, not the PHP include code. Just in case that matters to you at all.
While Taltos' idea of making a template works for a while, it falls apart if you want to change the navigation. You still would have to go back and change everything so that it matches. With the PHP include way of doing it, one edit effects your whole site.