The Google AdSense extension allows to easily add Google AdSense advertisements to the sidebar of your wiki. This extension requires an account with Google's AdSense.
This is https://www.mediawiki.org/wiki/Extension:Google_AdSense extension.
Only two files have been modified - portlet label shouldn't be "Google AdSense": https://productforums.google.com/d/msg/adsense/8Z45KlD8CGo/XXXvIfaOVFYJ