The Light Warriors of 8-Bit Theater: Red Mage is sanguine (emphasis on arrogant and self-indulgent); Thief is choleric (emphasis on narrow-minded and obsessive); Fighter is phlegmatic (emphasis on lazy and reactionary); and Black Mage is melancholic (emphasis on independence and perfection).
There are a lot of characters in the Web Animation series The Bear Show, so they have their own Temperaments: Mario, John Cena and Peter Griffin (sanguine and choleric), Randy Orton, Stewie Griffin, Sheriff Woody, Link and Alberto Del Rio (choleric), Luigi, Daddy Bear, CM Punk and Star (sanguine), Triple H and Pikachu (melancholic), Kirby (phlegmatic), and Toad (eclectic).
Cry Havoc features Skoll as sanguine, Karcharoth as choleric, Hati as melancholic, and Fenrir as phlegmatic. These characteristics seem to drive them apart more than unite them, as is normal.
Ctrl+Alt+Del: Ethan (sanguine), Lucas (melancholic), Lilah (choleric), and Zeke (phlegmatic).
Looking at the the questing team in Digger, The Shadowchild (sanguine), Grim Eyes (choleric), Murai (melancholic), and Digger (phlegmatic).
The eponymous doctors of The Dragon Doctors: Sarin (sanguine), Goro (choleric), Mori (melancholic), Kili (phlegmatic), and Aki (eclectic). Fittingly, they were also compared by the artist to Air, Fire, Earth, and Water, respectively, matching the Four Temperments' elemental affiliations.
The Dreamer: Alexander (choleric), Beatrice (sanguine), Nathan (melancholic), and Alan (phlegmatic).
Electric Wonderland: Trawn (choleric), NJ (melancholic), Shroomy (phlegmatic), Aerynn (sanguine).
The cast of Exterminatus Now fits pretty nicely, going by the negative traits (because really, they have no others): East (sanguine), Lothar (choleric), Virus (melancholic), and Rogue (phlegmatic).
The Help Service from Hell(p): № 1 is choleric (competitive and overbearing leader), № 4 is phlegmatic (quiet, patient, and gentle), Marcus is sanguine (outgoing and oversexed drama queen), and Domino is melancholic (cynical and cold).
Homestuck: John (phlegmatic), Rose (melancholic), Dave (choleric), and Jade (sanguine).
And among the Midnight Crew: Spades Slick (choleric), Clubs Deuce (sanguine), Diamonds Droog (melancholic), and Hearts Boxcars (phlegmatic).
Among the trolls: Nepeta, Terezi and Feferi (sanguine); Karkat, Vriska and Eridan (choleric); Aradia, Kanaya and Equius (melancholic); and Tavros, Sollux and Gamzee (phlegmatic).
In the Alpha kids: Jane (phlegmatic), Jake (choleric), Roxy (sanguine), and Dirk (melancholic).
The Inexplicable Adventures of Bob!: Bob (phlegmatic), Jean (melancholic), Molly (sanguine), and Voluptua (choleric). Albeit, Jean certainly has the hair-trigger temper of a choleric.
Keychain of Creation: Misho (melancholic), Marena (choleric), Ten Winds (phlegmatic), and Secret (eclectic).
M9 Girls!: Any (melancholic), Pato (phlegmatic), Clau (sanguine), and Karla (choleric).
Monsterkind: Roy (sanguine), Molly (choleric), Kip (melancholic), and Wallace (phlegmatic).
Narbonic: Helen (sanguine), Mell (choleric), Dave (phlegmatic), and Artie (melancholic).
The Big Lez Show: Lez i0 (choleric), Sassy (phlegmatic), Norton (sanguine), and Clarence (melancholic).
The four main characters of the Web Animation series Broken Saints fit fairly well: Oran (choleric), Kamimura (melancholic), Raimi (phlegmatic), and Shandala (sanguine).
Albeit, Shandala doesn't quite fit any of them, but her bright, cheerful, and compassionate nature recommend her most to sanguine.
An entire episode of the webseries CrackedAfter Hours is devoted to discussing how many famous groups of four adhere to this schema, even describing several groups already listed on this page (though it's worth noting that they have misattributed the sanguine qualities to choleric characters, and vice versa). As they are also a quartet, they even describe themselves (indirectly, through analogy to the Teenage Mutant Ninja Turtles).
By their definition: Michael (sanguine), Dan (phlegmatic), Soren (melancholic), and Katie (choleric).
The main fighters from Dragon Ball Z Abridged each fit one or one combination: Goku (sanguine + choleric), Vegeta (choleric), Tien (choleric + melancholic), Piccolo (melancholic), Gohan (melancholic + phlegmatic), Krillin (phlegmatic), Trunks (phlegmatic + sanguine), Chiaotzu (sanguine), and Yamcha (eclectic).
Game Grumps/Steam Train: Jon/Danny (sanguine), Arin (choleric), Ross/Suzy (phlegmatic), and Barry (melancholic).
Hitler Rants Krebs (sanguine), Hitler (choleric), Jodl (melancholic), and Goebbels (phlegmatic).
Homestar Runner's House of Strong: Strong Bad (choleric), Strong Mad (sanguine), Strong Sad (melancholic), The Cheat (phlegmatic).