A Christmas Carol: Ebenezer Scrooge (choleric), The Ghost of Jacob Marley (melancholic), The Ghost of Christmas Past (eclectic), 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).
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).
Also the four Marauders: James Potter (choleric), Sirius Black (sanguine), Remus Lupin (melancholic), and Peter Pettigrew (phlegmatic).
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 (choleric), Ron (sanguine), Hermione (melancholic), and Neville (phlegmatic).
The Weasley family: Arthur and Bill (phlegmatic), Molly and Ginny (choleric), Charlie (eclectic), 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).
On the Road: Sal Paradise (sanguine), Dean Moriarty (choleric), Carlo Marx (melancholic), and Marylou (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).
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.
Also, the later books have the four eldest Marshall brothers: Joe Jr. (choleric), Jack (phlegmatic), Bobby (sanguine), and Ted (melancholic).
Sammy Keyes and her friends: Sammy (choleric), Dot (melancholic), Marissa (phlegmatic), and Holly (sanguine).
Carmen, Tibby, Bridget, and Lena spend their first summer apart in The Sisterhood of the Traveling Pants. Carmen snaps and gets mad (choleric) so she comes home expecting Tibby to understand because Tibby walks around screaming, "Screw the world" because that's easier than feeling something (melancholic). Carmen and Tibby visit Bridget who talks about her mother and she tells her friends that she just wants to feel good and happy and alive (sanguine). The last one to join them is Lena who feels so sad that people like Kostas and Bridget who have lost everything can still be open to love while she, who has lost nothing, is not (phlegmatic).
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).
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).
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).
In Todd Strasser’s Wildlife trilogy, boy howdy are the Coming Attractions a textbook example: Gary (choleric), Susan (phlegmatic), Oscar (sanguine), and Karl (melancholic).
The Wonderful Wizard of Oz: Scarecrow (choleric), Nick Chopper/The Tin Woodsman (melancholic), Lion (sanguine), and Dorothy (phlegmatic).
In "Överenskommelser", we have Beatrice as the Sanguine, Seth as the Choleric, Sofia as the Phlegmatic and Johan as the Eclectic.
In ''De skandalösa", Magdalena as the Melancholic, Gabriel as the Sanguine, Venus as the Phlegmatic and Ossian as the Eclectic.
In The Anderssons by Solveig Olsson-Hultgren, you can see the four original Andersson sisters as this: Elin is the Choleric, Mandi is the Phlegmatic, Ida Sofia is the Melancholic and Greta is the Sanguine.