Belgium's Tomorrowland 2012
A giant straight version of a circuit party: "More than 180,000 visitors attended one of the most beautiful and talked about festivals in world. The 8th edition of Tomorrowland was one that would never be forgotten. An amazing festival, a magic location, wonderful decor, more than 400 artists and by far the best public in the world!" Wikipedia claims that all 180K tickets sold out in one day, leaving two million people on waiting lists.
(Tipped by JMG reader Ray)