For the last 2 years we spent most of our time providing our services to DPG Digital Media, creating and maintaining a number of news portals based on the Joomla! CMS.
We recently helped Greek Educational College IEK-XINI to move their website to the Joomla! CMS. They needed a simple system to manage the regulary updated content but most of all they wanted this inhouse.
Joomla! has already a native component dealing with banners and pretty much it does the job. But if you need more than that, you have to use a more sophisticated solution like Google ad manager, aka Doubleclick for Publishers (DFP).