"Circles are sized by the number of medals that countries won in summer Olympic Games. Use the slider to view past Olympics, or click on a country to display a list of its medal winners."
(The New York Times)
[Interestingly although the map appears to have been created as a simple representation of the global medal tally the map also quite eloquently reveals aspects of the changing economic fortunes and political leanings of particular countries. Note for example Germany''s Olympic success prior to the Second World War and Eastern European success during the Cold War.]
http://www.nytimes.com/interactive/2008/08/04/sports/olympics/20080804_MEDALCOUNT_MAP.html
http://2010games.nytimes.com/medals/map.html