From a press release:
March 28, 2009: At 8.30pm local time tonight, 2848 cities and towns across 83 countries will switch off their lights for Earth Hour in a moment of global solidarity.
From the small island nations of the South Pacific to the densely populated cities of the Americas, millions of people from all walks of life and corners of the world will participate in Earth Hour, casting their vote in the world’s first global election between Earth and global warming.
66 national capitals and 9 of the10 most populated metropolises on the planet have confirmed their participation in this year’s event, along with some of the world’s most prominent cites.
Here is the list of cities and more information.