I've recently reread Chandler's The Big Sleep, and watched both the Bogart and Mitchum film versions (the Bogart movie is better, but the Mitchum version sticks closer to the original plot, with the minor exception of relocating the whole thing to England). And I started wondering who you'd cast in a modern remake, notwithstanding the comment I saw recently that The Big Lebowski is loosely based on the same plot. I am thinking, perhaps coloured by his performance in Blade Runner, that Harrison Ford would have made an excellent Marlowe at some point in the 90s, but maybe not so much now. Johnny Depp might be able to carry it off, although I don't think he's quite worn-looking enough. Geoffrey Rush, on the other hand, is probably too worn-looking. James Caan did a good enough version in Poodle Springs in 1998, but his Marlowe was deliberately an older version since some of that movie is about how times have moved on past the character. I'm not going to canvas for further suggestions here, but I do think it's an interesting question.