EYE OF THE DEVIL - Gary McFarland - Very impressive, jazz tinged, score for unconventional fright flick.
This is the first one that came to mind for me too. Probably my favorite FSM release as it was a totally new and welcomed discovery for me.
I was previously aware of Gary McFarland's jazz work, but not this score...although I wouldn't really consider McFarland a film composer per the title of this thread, but rather a jazz composer-arranger/musician who dabbled in film a couple of times before his untimely death. Still, this is my pick.
How about Ferde Grofe's ROCKETSHIP X-M and THE RETURN OF JESSE JAMES? And Aaron Copland's THE RED PONY? All of these are fine scores by two non-film score composers.
I don't think Newman really qualifies and I myself wouldn't count Copland either. He was Oscar-nominated multiple times for his film music (winning once) and though he wasn't primarily a film composer he did write eight film scores! That's half as much as Korngold (who did 16), whose reputation lasted because of his film scores after most of his classical stuff was forgotten (we're talking before the modern Korngold revival, of course).
I'd say Copland is borderline for inclusion but definitely not Randy Newman.
