A Christmas Carol: Ebenezer Scrooge (choleric), The Ghost of Jacob Marley (melancholic), The Ghost of Christmas Past (leukine), The Ghost of Christmas Present & Tiny Tim (sanguine), Bob Cratchit & The Ghost of Christmas yet to come (phlegmatic).
A Clockwork Orange: Alex (melancholic), Dim (sanguine), Georgie (choleric), and Pete (phlegmatic).
A Separate Peace: Gene (phlegmatic), Finny (choleric), Leper (sanguine/leukine), and Brinker (melancholic).
American Gods: Shadow (phlegmatic), Mr. Wednesday (choleric), Czernobog (melancholic), and Mr. Nancy (sanguine).
The original four members of The Baby-Sitters Club: Kristy (choleric), Mary Anne (melancholic), Claudia (sanguine), and Stacey (phlegmatic).
The Bailey School Kids: Eddie (choleric), Liza (melancholic), Howie (phlegmatic), and Melody (sanguine).
In The Bible, a case can be made for the first five kings in David's dynasty: David (sanguine), Solomon (leukine), Rehoboam (choleric), Abijah (phlegmatic), and Asa (melancholic).
In Jesus' parable, the wealthy father (sanguine), his dutiful elder son (melancholic), and the prodigal son (choleric).
The Two Evangelist Duos from Acts: Paul (choleric), Mark (melancholic), Silas (phlegmatic), and Barnabas (sanguine).
The four Pevensie Children in The Chronicles of Narnia: Peter (choleric), Edmund (melancholic), Susan (phlegmatic), and Lucy (sanguine).
Also the four Marauders: James Potter (melancholic), Sirius Black (choleric), Remus Lupin (phlegmatic), and Peter Pettigrew (sanguine).
Four of the prominent professors, as well: Sybill Trelawney (sanguine), Minerva McGonagall (choleric), Severus Snape (melancholic), and Albus Dumbledore (phlegmatic).
And for the main cast: Harry (melancholic), Ron (choleric), Hermione (phlegmatic), and Neville (sanguine).
The Weasley family: Arthur and Bill (phlegmatic), Molly and Ginny (choleric), Charlie (leukine), Percy (could not be more melancholic if he tried), Fred, George, and Ron (sanguine, especially the former two).
The D Squad in The Homework Machine:Kelsey (sanguine), Snik (choleric), Judy (melancholic), and Brenton (phlegmatic).
The Horus Heresy novels, set in an earlier era of Warhammer 40,000, toy with this openly with Warmaster Horus' inner advisory circle during the first few novels, consisting of Ezekyle Abaddon (choleric), "Little Horus" Aximand (melancholic), Tarik Torgaddon (sanguine), and Garviel Loken (phlegmatic).
In In the Time of the Butterflies by Julia Alvarez (a dramatization of the lives of the Mirabal sisters from the Dominican Republic), Maria Teresa "Mate" Mirabal (sanguine), Minerva Mirabal (choleric), Dede (melancholic), and Patria (phlegmatic).
The four boys in the camp plot of Jelly Belly: Protagonist Ned (melancholic), Richard (choleric), Hog (phlegmatic), and Max (sanguine).
In The McGurk Mysteries, the original four kids in the McGurk Detective Agency. Jack McGurk (Choleric), Joey Rockaway (Melancholic), Willie Sandowski (Phlegmatic), and Wanda Grieg (Sanguine).
The Monkey Wrench Gang: Doc Sarvis (sanguine), Hayduke (choleric), Smith (melancholic), and Abbzug (phlegmatic).
On the Road: Sal Paradise (sanguine), Dean Moriarty (choleric), Carlo Marx (melancholic), and Ed Dunkel (phlegmatic).
Phantom's Reckoning 2: Yuki (melancholic), Kaori (phlegmatic), Shoji (sanguine with some choleric), and Tatsuya and Makoto (choleric).
In The Poisonwood Bible, the Price ladies minus Ruth May fit this: Rachel (sanguine), Leah (choleric), Adah (melancholic), and Orleanna (phlegmatic).
Jane Austen's Pride and Prejudice — Bennet family: Lydia and Mrs. Bennett (choleric), Mary (melancholic), Jane and Mr. Bennett (phlegmatic), Kitty (sanguine), and Elizabeth (leukine).
The men: Mr. Darcy (choleric/melancholic), Mr. Collins (phlegmatic), Mr. Bingley (sanguine), and Mr. Wickham (leukine).
In Red Mars, psychologist Michel Duval slots the classical temperaments into his own psychological theory: Sanguine = Extroverted + Stabile; Choleric = Extroverted + Labile; Phlegmatic = Introverted + Stabile; Melancholic = Introverted + Labile.
The Roman Mysteries: This is actually explictly stated in the books, which is justified because it takes place during a time period when doctors still believed in the four humors.
The four protagonists of Sleepers by Lorenzo Carcaterra: Michael (choleric), Tommy (melancholic), John (sanguine), and Shakes (phlegmatic). Interestingly, the four abusive guards at the reform school fit this paradigm rather neatly as well: Nokes (choleric), Styler (melancholic), Addison (sanguine), and Ferguson (phlegmatic).
The four Compson children in The Sound and the Fury count. Caddy (sanguine), Jason (choleric), Quentin (melancholic), and Benjy (phlegmatic).
The Star WarsExpanded Universe, in the four pilots of the X-Wing Series: Wedge (choleric), Tycho (melancholic), Wes (sanguine), and Hobbie (phlegmatic). During Starfighters of Adumar, they even get appropriate identifiers; respectively, "the diligent one," "the doleful one," "the darling one," and "the dour one."
Done deliberately by Émile Zola as a character study in Thérèse Raquin. Laurent (sanguine), Mme. Raquin (choleric), Camille (phlegmatic), and Thérèse (melancholic).
The Three Musketeers: Aramis (phlegmatic), Porthos (choleric), Athos (melancholic), and their sidekick D'Artagnan (sanguine).
Or d'Artagnan as choleric and Porthos as sanguine.
Tale of the Troika: not the protagonists, but the members of the Troika: Vunyukov (phlegmatic), Farfurkis (melancholic), Khlebovvodov (choleric), Vybegallo (sanguine).
The Night Lords of Warhammer40000 are introduced. The lineup for First Claw at the beginning Soul Hunter played for the worst of each humor, because to do otherwise wouldn't be Grimdark.
Choleric — Uzas. His emotions are all or nothing; he's almost universally violent, irritated or sullen when he isn't an unreadable shell. Thinks only of himself, which is how he became corrupt in the first place. He himself admits he all but runs on a slow, seething rage.
Melancholic — Xarl. Cynic, chronic complainer, suspicious pessimist, and yet somehow a very capable Lancer for Talos. Throws his whole life into the sword and it shows in every sense of the word.
Phlegmatic — Talos. His romanticism of his Legion's past and the power his prophetic abilities have over his life have left him worn thin all around. Known to brood over both. His stubbornness won't let him put anything less than his heart and soul into what he does however, and it's nearly killed him before.
Sanguine — Cyrion. Possibly the most easygoing of the group, and the most vocally distressed at the state of the Legion, although it also means he stands out the least in the shambling wreck of a squad.
Her Orphans series also has this, although it's not as pronounced: Janet/Butterfly (definitely phlegmatic), Crystal (probably melancholic), Brooke, narrator of the final book in the series (best fit as sanguine), and Raven (melancholic and choleric).