Here are some historically significant videos.
Until Psy broke the record with Gangnam Style, this 2004 lip-sync-in-the-bedroom was the number one all-time video, with over 700 million views. The performer is Gary Brolsma from New Jersey and his pure exuberance and joy at just having playful fun with music really connected with folks. This Wikipedia page provides more info.
The next video is a really interesting introduction to “the anthropology of YouTube” given by Professor Michael Wesch at the Library of Congress, June 23rd 2008. If you want to better understand “why” YouTube and other Web 2.0 technologies are so successful, this presentation will definitely help.