Nothing has been released yet - but it WILL be out before the end of the year, that much we know.
Many people are thinking November or December, around the same time the other Superman DVDs are due to come out (Superman II: The Donner Cut, Superman Returns, etc.).
As soon as TVshowsonDVD sends the e-mail out notifying us all of the date - I guarantee you several people will jump to post it here - as has happened with the last 3!
