http://en.wikipedia.org/wiki/List_of_most_watched_television_broadcasts#World
According to Wiki.. The most watched event (people watching at the same time) was the opening ceremony of the 2008 Olympics in China, between 1-4 billion. Next was the 2006 World Cup final although exact numbers are hard to predict..
The moonlanding in 1969 - viewed by 14% of total population of the world at the time. 530 million
An Elvis concert in Hawaii?? Really? Apparently the Japanese and Philippinos were huge fans.
A 2011 cricket match between India and Pakistan and finally a Eurovision Song contest finale.
The most watched show in the US - the Mash Finale, Dallas Finale, Roots then a Superbowl game.
In Canada - the Olympic hockey final in 2010 - half the pop.
Oz - 2005 Australian Open - 2003 Rugby Final - Masterchef
UK - 1966 World Cup Final (England - Germany) - Diana's Funeral, Eastenders - a divorce...?
Germany - 2010 World Cup Final
So now you know..