This is something I've thought about a lot:
Dresden: Tough... I think Brendan Fraser could work (he's tall, but not thin... but I think he could do the character)
Murphy: Either Maggie Lawson from Psych
-or (going on body type)-
Jamie Eason (girl next door, and all springy muscle that doesn't preclude feminine curves)
Thomas: Brad Pitt (I'm thinking Fight Club vintage), but Matt Bomer could work too.
Lara: Angelina Jolie. And she does "wanton, predatory sexuality" really well (and with Mr. & Mrs. Smith/Tomb Raider/Wanted, audiences would believe the action sequences)
Kincaid: Christian Kane (Eliot on Leverage... he may also work for Micheal)
Justine: Megan Fox (if she can do vaguely innocent)
Ebenezar: Sean Connery. Old, badass Scott... yep.
Marcone: George Clooney
Hendricks: Some pro wrestler (Triple H?)
Gard: Lucy Lawless
Bob's Voice: Hugh Laurie
Micheal: dunno
Sanya: Micheal Clark Duncan (a voice-over could fix the accent if he can't do a decent Russian accent)
Butters: Steve Buscemi (with some makeup to make him look younger).
Nicodemus: I want to say Alan Rickman (because everything's better with Alan Rickman), but while he could certainly do "souless evil", I'm not sure if I could buy him as a neigh invincible engine of destruction. Maybe Hugo Weaving?