I have only a dozen of his scores and from those I'd say my favourites are:
- La Vergine di Norimberga (The Castle of Terror) (1963) - Fratello Sole, Sorella Luna (Brother Sun, Sister Moon) (1972) - Fantasma d'Amore (1981) - The 7th Dawn (1964) - Il Giorno Del Furore (Fury) (1973)
but the one I'd really like to get - from those old vinyl LP days - is Buona Sera, Mrs. Campbell (1968)
I also like his theme from The Valachi Papers (1972) - as with all of his works there are great themes.
I have always wanted to see A REASON TO LIVE, A REASON TO DIE. I love the main gorgeous theme. The full treatment starts at about 2:30 in the youtube below.
Not a score but I think the Oscar nominated song he wrote for Madron called Till Love Touches Your Life is one of the most beautiful love songs written for a film.