From all of the unreleased Bernstein scores I've heard (there are so many I haven't heard yet), "The Amazing Mr. Blunden" (1972) is my favorite. A masterful and beautiful work, it's well worth watching the movie just to hear Bernstein's score.
Has anybody heard "Saturday's Hero" (1951)? It's Bernstein's first score, and I'd love to know what some think of it. The film isn't easy to track down but it has been broadcast on TV.
Has anybody heard "Nightmare Honeymoon" (1974)? Seems to be of the few horror films Bernstein scored, I would love to know how it is. The film is available on Warner Archive.
On YouTube I found some excerpts from unreleased scores. A little something for everyone: a romantic and intense 1950s noir score, a 1970s pop-influenced score with Elmer's trademark rhythmic writing, and a glorious symphonic 1980s score. All three of these, if they exist, ought to be released!
"The Amazing Mr. Blunden" (1972) is on YouTube. Go to the 5:53 mark for a lovely and mysterious cue that underscores a discussion about ghosts. But there are many brilliant and lovely, sensitive Bernstein cues in this score, which for me is the zenith of his unreleased work (that I'm familiar with, at least - going through his filmography it's staggering how many I haven't heard, but this is the cream of what I've heard).
Roger Feigelson has written on the Intrada boards about this: "I've located elements but the licensing issue is extremely challenging. But I keep trying." That was almost two years ago. Hopefully this will see a release someday.