I've recently finished the Mistborn trilogy by Brandon Sanderson and at the very end of the book:
Sazed tells Spook: "P.S. There are still two metals that nobody knows about. You might want to poke about and see if you can figure out what they are. I think they'll interest you."
Is there a reliable answer to what they are and what they do? If there is another book to read that answers this please let me know.