A few inspiring and personal favorite viral videos that I have come across. Focusing on viral ad campaigns.
http://www.youtube.com/watch?feature=player_embedded&v=R55e-uHQna0 - VW ad campaign, promoting new features for an upcoming model of their brand.
http://www.youtube.com/user/Blendtec/videos?sort=dd&view=u&page=2 - Blend Tec is still existent on YouTube, and has been for a few years now. They promote their Blenders by blending mainly gadgets and electronics and items suggested by viewers. They way the blender will blend anything from an iPad to SLR camera's shows the quality of their products.
http://www.youtube.com/watch?v=-nYhixp7bXI - The Berocca advert is the most recent Viral Ad, something really out of the ordinary but it works with the flow and editing of the video along with the music! Very catchy!