It´s been around in thousands of blogs already but i decided to share you this one too.
For HTML
<meta HTTP-EQUIV="REFRESH" content="0; url=http://www.yourdomain.com/index.html">
Note that “0″ – is in seconds, how fast your site will be redirected.
For PHP
<?php header( 'Location: http://www.yoursite.com/new_page.html' ) ; ?>
Note that this will not work if you have html tags before that.