Mac vs. PC (2009)
Synced ads -- or the idea that two ads on the same page (a 728x90 and 300x250, for example) above the fold would communicate with each other -- had been around for a while. In fact, the technology is something that we pioneered during my days at PointRoll. At the time, we were using Flash local objects to get one banner to cause a change in the other banner, and it was pretty cool stuff. Though some of the examples were notable, they were nothing compared to what Apple wowed us with a few years later.
In this campaign, the two ads used video to take the Mac vs. PC television campaign to a new peak of interactivity and ingenuity. The PC would crawl out of one banner and into another, the Mac would look up at him as he carried out his antics, and we would be inspired to think of the page in front of us as a larger canvas that was able to carry a message beyond the borders of traditional banners. Even after compiling this list, I still long for more examples that use the medium to such a lofty effect as this campaign.