This is sort of an old thread, but I'm going to chime in with a couple ideas in hopes anyone still cares. I don't remember ALL the characters from the first trilogy (EDIT: I got most of the big parts I think), but I'll try to hit the ones I actually have an idea for...
For the early books,
Karl Urban as Kelsier,
Milly Alcock as Vin,
Idris Elba as Sazed,
Gary Oldman (my favorite actor) as The Lord Ruler,
Jaeden Martell as Spook,
Sam Rockwell as the bad guy mistborn who's name I forget (Elend's brother?),
Tom Hardy as Elend,
DJ Qualls as Vin's brother,
Paul Giamatti as Ten Soon/Renoux,
Elizabeth Dibicki as Tindwyl,
Danny Devito as Clubs,
Benicio Del Toro as Breeze,
Benedict Cumberbatch as Marsh,
Terry Crews as Ham,
Chris Pratt as Dockson,
Jeff Goldblum as Staff Venture.
For the Wax and Wayne series, I have fewer names. My casting is a bit old, but I'm expecting makeup and acting to close the gap:
Idris Elba returns as Harmony,
Paul Giamatti returns as TenSoon,
Timothy Olyphant as Wax,
Walter Goggins as Wayne,
Anna Kendrick as Marasi,
Keira Knightley as Steris,
Anthony Hopkins as Wax's uncle,
Kelly Reilly as his sister.
Bash away. I'm sure I'll be mocked for a few of those choices.