Imperiex for the win. He was like... Galactus... but without the jobber.
Hell, it took a superman amped up by deus ex machina to PUSH Imperiex through a wormhole, to the big bang... which was pretty much the only thing that really hurt/killed him.
BTW... wth is classic mean. Imperiex Bloodlust destroys the earth before anyone can do anything. 99% of the heroes die. Hulk and Thor and left floating in space wondering what they can do to Imperiex.