Ray Bans
http://urbanpeek.com/wp-content/uploads/2011/06/7.-ray-ban1-1024x248.jpg
People wore the glasses and were staring at a billboard in an attempt to get people to see the ad.
T-Mobile
http://www.youtube.com/watch?v=VQ3d3KigPQM
This is a HUGE performance flash mob, but because it is to promote the company's service, it becomes.... advertising! I like how quickly it grows, and how 'audience members' are part of it and slowly add to the size of the mob.
Dodge
http://www.youtube.com/watch?v=t4VWPq__1vo
I like how they appear a part of the crowd, then slowly identify themselves by the shirts under their jackets.