This is my list of characters I like to see in the sequel Man of Steel, do not know if the producers or the director to pay attention to this list of suggestions, but nothing to lose by trying:
Lex Luthor (principal):
It is the most powerful man around Metropolis, is corrupt and deceitful, has political ambitions, is the opposite that is Superman and CEO of LexCorp, Metropolis practically has all under his command, from the mafia to the Mayor
Also deserves an adaptation that does justice after Kevin Spacey's interpretation in the film Superman Returns
Doomsday (secondary):
It is the Last and Ultimate Kryptonian Weapon of Destruction, was used by Zod and Brainiac to destroy Krypton before the arrival of the Earth Kal-El/Superman
He is rescued by Lexcorp employees who try to use along with the government as a weapon to destroy Superman definitely, because they do not trust an alien who has many powers and also bills itself as the planet's savior
But they were out of hand, destroying everything in its path until finally in Metropolis Superman encounters unleashing an epic battle that will show the sacrifice you are willing to do to save Metropolis Superman and everyone
A sacrifice that can lead to the "Death" of maximum superhero on the planet, but not unique in its struggle to defend truth and justice
John Corben/Henry Ackerdson/Metallo (cameo):
in my opinion its presence should be minimal, just reduced to cameos, like the Scarecrow/Jonathan Crane (Cillian Murphy) in the Batman movies, then give at some future moment of glory his own solo
Brainiac (references):
in my opinion its presence should also be minimal, but smaller than that of Metallo, and then make the sequel with the main villain Darkseid
referrals can be made as Lex Luthor and Lexcorp secretly working with the government in some form of artificial intelligence in the film Man of Steel