I have thought this over many a time for this is the greatest book ever and I have come to the conclusion that you could never cast it right ever because everyone takes each character so personally but if I had to cast it I would go with the following:
Jay Gatsby: Christain Bale Daisy Buchanan: Amy Adams Nick Carraway: James McAvoy Myrtle Wilson: Ginnifer Goodwin Tom Buchanan: Daniel Craig Jordan Baker: Carla Gallo Meyer Wolfsheim: (could be) Daniel Day-Lewis (question would be would he ever take such a small role?) or Peter Stormare
I totally agree with armsofsnakess about Daisy, Nick, and Myrtle, especially Myrtle... for some reason I always pictured Ginnifer Goodwin as she is curvy and has the "vitality" that Nick describes her as having... James McAvoy would be a great Nick; thoughtful, sweet, subtle. And Amy Adams has that kind of airy almost annoying quality that Daisy has.
Daisy - If she were a little younger, definitely Nicole Kidman! But she's so gorgeous, she could probably still pull it off. She could really portray this ditzy girl while still showing her deeper layers. ... :) Or Reese Witherspoon because she seems so genuinely sweet, and I'd really like to see her in a serious role. :) Third choice would be Keira Knightley. :)
Gatsby - I think Hugh Jackman would be an amazing Gatsby! He just seems like a total sweetie but also very cool and a little mysterious, at the same time. :) And being absolutely gorgeous doesn't hurt. :) Or Robert Downey Jr! I know, he's a little into the whole actiony stuff right now, but I've seen him serious and he has serious acting ability. :)
Nick Carraway - Ewan McGregor. :) Because he has that goofy quality, and Nick was a smart character but a bit naive, and just happened to accidentally stumble into this whole story.
Jordan Baker - Natalie Portman (if Daisy went to Keira or Reese. :)) Or Rachel Weisz? Both are beautiful and sophisticated. Third would be Julianne Moore!
Tom Buchanan - Joaquin Pheonix, I think. He's played arrogant, obnoxious characters before while still allowing the audience to feel compassion for him,
Myrtle - Cate Winslet! I love her because she's not classically beautiful, but she has a confidence and charisma that totally make up for it. She's my ideal Myrtle. :) Runner up would be Maggie Gyllenhaal.
Myrtle Wilson is a “thickish figure of a woman” in her “middle thirties”. Even though she is not very beautiful, she still seems attractive. Casting suggestions for Myrtle such as Nicole Kidman or Naomi Watts are just ridiculous!!
Ginnifer Goodwin or Kate Winslet are much more thoughtful suggestions.
Jordan Baker is a professional golfer, so the actress who plays has to at least look like a sportswoman! Keira Knightley or Rachel McAdams might be okay.
I like Natalie Portman for Daisy, although her intelligence might not be a good fit for the part.
Nick: Adrien Brody Tom: Will Ferrell (Don't laugh - he could play big and dumb!) Jay: David Wenham
Hmm Lee Pace would be pretty good...nice and mellow, a good actor. How old is he, 30? That's actually a really good fit for Nick. I think I switch to him hahaha.
Sometimes I doubt your commitment to Sparkle Motion.
Gatsby - Johnny Depp Daisy - Undecided on this one. Nick - Daniel Day Lewis Tom - Russell Crowe
I also have an "old-time" cast:
Gatsby - Cary Grant Nick - Montgomery Clift Daisy - Elizabeth Taylor (Daisy doesn't necessarily have to be blonde.) Tom - Clark Gable Jordan - Vivien Leigh Wilson - James Dean Myrtle - Any odd-lookin' chic of the time would do.