In addition to enjoying films for their own sake, I also like to analyze the way films tell stories. There is a good deal of common ground with the way books tell their stories, but there are things unique to each medium. This is not to say one is superior to the other, only that you can (and can't) do things in books that you can't (or can) do in films, and vice versa.
Adaptations of books into films fascinate me, because so often the work suffers in translation - yet when it does work, it's amazing. Take a look at the book and film of L.A. Confidential. Both are masterpieces in their own right. The film covers only a fragment of the novel's plot and scope, yet does such a good job of distilling the key characters and conflicts down to the essentials that one can enjoy both on their own terms.
How does this relate to writing craft? Whenever I write a book, I always try to come up with the perfect cast for an ideal movie (or TV miniseries) adaptation. Although I will use these cast members when I visualize the story in my head, I don't incorporate this into the book's descriptions of the characters. (In fact, I'm trying to pare visual description of characters down to what's strictly relevant, thereby letting the readers get their own images.) It primarily comes in handy for writing dialogue. There have been several occasions when I needed to "hear" a character's dialogue in my head, imagining it in the actor's voice, before I was able to get the dialogue right.
It's not all work, of course. Casting the perfect film adaptation is just part of making what I call "mind movies." I'll also consider how key scenes would be portrayed in a perfect adaptation, or how to address plot or character issues without the benefit of exposition or internal monologue (I refuse to have characters make "thinking faces" while having voice-overs in my mind movies). It's a fun way to explore the different storytelling needs of the two mediums, and the mind movies are a fun way to kill time when I'm bored - one can only play "Do, Dump, or Marry" with the cast of Firefly* so often.
So for my amusement and, hopefully, yours, I offer my ideas for the casts of perfect adaptations of my books. In some cases I've suggested multiple actors, any one of whom would do a bang-up job. You'll see a lot of genre actors here, and there are even a few actors whose films I usually avoid, but include because they would be perfect in their assigned roles. Also, these casts are always changing as my other cinema-nerd friends make awesome suggestions, or as actors age out of certain roles and age into others. And I'd like to apologize to Sam Rockwell for being my go-to actor for villains who are smarter than others think but not as smart as they think they are. One of these days I'll cast you as a nice guy, I swear.
Don't know some of these names? Look them up on Internet Movie Database!
Drew - Guy Pearce
Audrey - Linda Hunt or Kathy Bates
Margo/Lara - Rosario Dawson
Evie - Michelle Williams
Jones - Robert Downey Jr.
Doc Winslow - Jeff Bridges
Bannion - Brian Dennehy
The Day After Yesterday cast
Zack - Tom Waits, Sid Haig, or Danny Trejo
Elaine - Maggie Gyllenhaal
Daniel - Nathan Fillion or Ewan McGregor
Sarah - Naomi Watts or Sheryl Lee
Rachel - Liv Tyler, Kate Beckinsale, or Rachel Weisz
Mick - Matt Damon
Reg - Paul Williams
Tamara - Ellen Page
Dr. Howard - Jessica Harper
Wayne - Jason Mewes
Dr. Levinson - Brian Cox
Gina - January Jones
Rachel's mom - Carol Kane
Eskimo Sally - Sandra Oh or Jewel Staite
Marjorie - Caroline Williams
Greg - Sam Rockwell or Thomas Haden Church
Cecilia - Erin Brown
Ashes and Reckoning (putting these together into one adaptation)
Jennifer - Alison Lohman
Sean - Gary Oldman, Kevin Spacey, Tommy Lee Jones, or Paul Giamatti
Robert - Brian Cox or Morgan Freeman
Halsey - Edward Norton or Tom Cruise
Suzanne - Amber Benson
Alex - Bruce Campbell
Doug - Bill Moseley
Beatty - Rutger Hauer
Mr. Bradbury - Ian Holm
Anna - Amy Adams
Richard - Kurt Russell, George Clooney, or Jeff Bridges
Steve - Sam Rockwell
Eddie - Eminem
Gene - Aaron Eckhart
Deirdre - Jennifer Carpenter
Monique - Diane Lane or Virginia Madsen
Nick - Nathan Fillion
Leo - Michael Rooker or Adam Baldwin
Juliette - Juliet Landau, Monica Bellucci, Famke Janssen, or Melanie Laurent
I can't think of anyone to play Walt. Readers, please feel free to suggest someone to play a cowardly weasel!
These suggestions are only for the moderate-to-major roles in each book. There are still plenty of roles that a movie or miniseries would need to fill, but my knowledge of actors isn't encyclopedic enough to do that.
And these are just my own preferences of course, and subject to my own whims and tastes (note the heavy reliance on Joss Whedon alumni). When you read, feel free to use your own ideas when you imagine what the characters look and sound like. This is all just fun on my part, but it helps with my process, so it's all good.
*If you must know:
Do = Jayne, Shepherd Book
Dump = Simon, Wash
Marry = Oh Captain my Captain