Over the past 3 months I've attended the Joomla World Conference, WordCamp Orlando and DrupalCon Sydney.... all 3 of these content management systems off the ability to create large scale websites. They are all open source so they are free, you may have to pay for certain plugins, extensions or modules to customize your site to the desired product. But I recommend any of them to build a high quality professional grade website on.
Talking about big fishes, this is from the source code of time.com : <meta name="generator" content="WordPress.com" /> Not that hard to find out ain't it ? So proud to be a wordpress user hehe
Take a look on our article http://www.itera-research.com/which-cms-will-be-crowned-content-king-in-2015/
In greece, two popular sites are esos.gr and gialia.net.gr. The first one is Drupal and the second on symfony.