Someone safe, who also actually looks her age -- Rachel McAdams.
I'm gonna throw in the Olivia Wilde card into the casting hat.
Lois Lane-Olivia Wilde
Lex Luthor-Jon Hamm
General Zod-Jude Law (although I dont remember if Zod being in was a rumor or not)
Perry White-Hugh Laurie
Jimmy Olson-Charlie McDermott from ABC's The Middle