A fascinating thread. Many admirable novels have already been proposed as candidates for moviedom, but here are a few more suggestions.

Confessions of a Justified Sinner - James Hogg
A Hero of Our Time - Mikhail Lermontov
The Light and the Dark - C P Snow
Stranger in a Strange Land - Robert Heinlein
The Left Hand of Darkness - Ursula LeGuin
The Satanic Verses - Salman Rushdie

And as for non-fictional sources - how about a bio-pic of Bob Copper, based on "A Song for Every Season"?

Wassail!