Request domain name

I would like to be able to request the domain name. How can this be achieved without hardcoding it? $_SERVER['REQUEST_URI'] doesn't provide me the domain name, it just provides me "/index.php?page=2000" instead of e.g. "www.blaat.com/index.php?page=2000" I can't seem to find anything on the php site to get the domain name as well. I prefer using absolute URI's. The reason why this is a problem for me is besause I'm working on a site which has two different URI's but both display the exact same site. Cheers, Age Bosma