Star Wars Episode 3: Revenge Of The Sith Easter Egg - Anakin's Fate Revealed

The egg can be found at the part when the Chancellor and Anikan have a talk and they get to this weird energy thing (the Chancellor tells everyone else to leave). Well, keep a close eye on the display of whatever it is when it is shown. Also, keep listening to the sounds it makes. The energy things will soon barely make out what seems to be... A mask of Darth Vader? Not only that but if you ignore what they are saying you can barely hear that famous breathing noise he makes!!

In a way, its ironic because this happens when the Chancellor is telling Anikan about the dark side; when Anikan realizes that he can save Padme if he joins the dark side.