If Man of Steel get's a sequel, what villain would you like to see? Me: I would go with Brainiac because i've always wanted to see Brainiac in a Superman movie and with CG animation these days, it could be possible.
If you're wondering who should play Brainiac, I was thinking about having Hugo Weaving or Ralph Fiennes. Hugo is good at being evil after seeing him as Red Skull in Captain America: The First Avenger and Agent Smith in The Matrix and Ralph can pull off a creepy voice and he is also good at being evil after seeing him as Voldemort in the Harry Potter movies.
I also think they should have his appearance just like his one from the comic-book mini-series: Justice and then during the final battle between him and Superman they can have him become muscular and wear armor kind of like his appearance in the animated direct-to-video movie: Superman Unbound.