Solution is PHP code which redirects all www requests to non www page. Since You are (should) use some general configuration or header file in Your web application, you can include this PHP code (very top of php page):

<?php // Removing WWW from URI with PHP http://simplemediacode.info/?p=136
if ('mediabox.lv' !== $_SERVER['HTTP_HOST']) {
header('Location: http://mediabox.lv' . $_SERVER['REQUEST_URI'], null, 301);
}
?>

It use build-in PHP header() function to redirect all requests to another page, in this case: non-www domain.

Simple!

Remove WWW from domain

# This will remove www from your domain
RewriteCond %{HTTP_HOST} ^www.mediabox.lv$ [NC]
RewriteRule ^(.*)$ http://mediabox.lv/$1 [R=301,L]

This is what I now use for all my domains – domain without www prefix.

Add WWW to domain

This probably is best for old domains like mine www.rolandinsh.lv

# This will remove www from your domain
RewriteCond %{HTTP_HOST} ^mediabox.lv$ [NC]
RewriteRule ^(.*)$ http://www.mediabox.lv/$1 [R=301,L]

Here is mine with RewriteEngine On (works on this hosting and both versions of GoDaddy hosting plans example1.com and example1.com/example2.com):

# This will remove index.html AND index.php from URL
RewriteCond %{THE_REQUEST} /index.(php|html) HTTP [NC]
RewriteRule (.*)index.(php|html)$ /$1 [R=301,L]

And Kaspar’s method without RewriteEngine On:

RewriteEngine On # remove this, if you have it already
RewriteCond %{REQUEST_URI} index.html
RewriteRule ^(.*)index.html$ /$1/ [R=301,L]

Purpose of this is to remove duplicate content from Internet.

[Update on 2010.03.30]

Please keep in mind that some web applications still need index.php file for installation scripts as referrers. So it’s good to keep it in mind and comment these line during installation process if it fails.

# This will remove index.html AND index.php from URL
# RewriteCond %{THE_REQUEST} /index.(php|html) HTTP [NC]
# RewriteRule (.*)index.(php|html)$ /$1 [R=301,L]