I've an Ubuntu Server that runs Apache w/ Virtual Hosts. I operate a website using the primary domain as "mydomain.com" and it is situated in /var/www/mydomain.com.

Presuming I own multiple domains (each having a different tld), what's the easiest method to make certain all of them indicate "mydomain.com" (the main site).

Quite simply, do you need to create an .htaccess file in /var/www which has multiple 301 redirects for sites like "mydomain.internet" and "mydomain.org" that could indicat "mydomain.com"?

Try something similar to this:

<VirtualHost 1.2.3.4:80>
    DocumentRoot /var/www/mydomain.com
    ServerName mydomain.org
    ServerAlias mydomain.net mydomain.info mydomain.me
    RedirectPermanent / http://www.mydomain.com/
</VirtualHost>