The Lost Ring ARG
The concept is pretty neat: Ariadne woke up blindfolded in a corn maze outside of Johannesburg with no memory, Olympic-calibur athletic skills, and a tattoo bearing the words "trovu la ringon perditan" -- Esperanto for "find the lost ring." She sets out to find what is happening to her, and discovers others with similar stories.
There's already a wiki, and the game will almost certainly spawn offshoot projects all over the net and physical world.
The Lost Ring is a global alternate reality adventure created in partnership between McDonald's, AKQA and Jane McGonigal. Designed in collaboration with the IOC, The Lost Ring invites players from across the globe to join forces online and in the real world, as they investigate forgotten mysteries and urban legends of the ancient games. The Lost Ring recognizes McDonald's historic sponsorship of the Olympic Games, and brings the spirit of the Games to people around the world.
It started a week ago and should run for around 6 months. Go check it out, and join up!