The Syphon Filter series witnessed an extensive advertisement campaign throughout the late 90s - early 2000's.
Syphon Filter 1
Syphon Filter 2
Syphon Filter 3
Syphon Filter: The Omega Strain
A notable web advert took the form of an interactive flash game. in early 2004, users who were signed up to receive emails from playstation.com received emails directing them to a webpage called agencyhq.com. AgencyHQ was a mockup of the ZEUS mainframe, a database used by the IPCA for storing agency information. In 2006 the site was taken down by Sony, but still exists on archive.org. Sadly the game is inaccessible after the login screen. All account information and registration services have been taken offline. It is unknown if these barriers are removable via some sort of programming.