La Resa Dei Conti in the epic final duel. Awesome tension-building music and the payoff to a major plot thread in musical form? Doesn't get much better than that.
He composed most of the music of the sci-fi/horror film The Thing (1982), including the iconic and incredibly foreboding main theme, which he created in collaboration with the film's director, John Carpenter. It may be shocking to learn that it actually got nominated for a Razzie, though like the rest of the film, it was originally hated by critics (who accused Morricone of being lazy and just copying John Carpenter's score for Halloween (1978)), and has been Vindicated by History.
Sergio Leone himself considered Once Upon a Time in America to have the best score of any of his films. A sample. Particularly awesome: Morricone's instrumentals of The Beatles' "Yesterday", which ultimately increases the poignancy of Noodles's reunion with Max. Also of note is "Poverty", which helps give the film its old-timey American wistfulness whenever it makes an appearance.
The film The Legend of 1900 is an entire movie about a pianist who lives on a cruise liner. And yet, for all the film's music, the piece that stands out is, although haunting and powerful, the most simple.
"Chi Mai", used as a leitmotif in Le Professionnel, is probably Morricone's most powerful Tear Jerker.
Cinema Paradiso is Ennio Morricone's most heartwarming score. The famous "Love Theme" however is misattributed to him when in fact it was composed by his son, Andrea.
The Golden Globe and Oscar-winning soundtrack of The Hateful Eight notably features the first Western score by Ennio Morricone in decades—especially unique as Quentin Tarantino is usually not one to "trust" composers to score original music for his films.