So many regular series, since the dawn of time, have had Halloween episodes, which I don't consider "specials." Still, I suppose I might as well at least list some of them, in passing. At least the ones I personally remember (even vaguely) seeing; surely there have been many I've seen that I've forgotten, and many more that I've never seen at all. I'm not going to be saying much of anything about the episodes here, so perhaps you'll find the links useful. But for some of the episodes, I may have said a bit about them in my annual Halloween journals. (Note: most of these episodes originally aired on or near Halloween, but some may have aired at other times of year. The important thing is whether Halloween itself is pertinent to the episode's plot.)

A-J

Key & Peele
Season 2: Michael Jackson Halloween (Amazon; A.V. Club; Hulu; IMDb; Wikia)
Season 3: Sexy Vampires (Amazon; A.V. Club; Hulu; IMDb; Wikia)
Season 4: Scariest Movie Ever (Amazon; A.V. Club; Hulu; IMDb)

Kim Possible
Season 1: October 31st (Disney+; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

King of the Hill
Season 2: Hilloween (Halloween Specials.net; Halloween Specials Wiki; Hulu; IMDb; TV Tropes; Wikia)

The Life and Times of Juniper Lee
Season 2: It's the Great Pumpkin, Juniper Lee (Halloween Wiki; IMDb; Wikia)

Lizzie McGuire
Season 1: Night of the Day of the Dead (Disney+; Halloween Specials Wiki; IMDb; Wikia)

Lucas Bros. Moving Co.
Season 2: Tales from the Hoodie (Hulu; IMDb) Not set on Halloween, but aired around then, and it's Halloweenish. (And it's set on Friday the 13th.)

Lucifer
Season 2: Monster (Amazon; A.V. Club; IMDb; Wikia)

Magnum P.I.
Season 2: Make It 'Til Dawn (Amazon; CBS; IMDb; Wikia)

Major Lazer
Season 1: Vampire Weekend (Hulu; IMDb) Not set on Halloween, but it originally aired around then, and it's Halloweenish.

The Mayor
Season 1: City Hall-oween (Amazon; Halloween Specials Wiki; IMDb)

Mixed-ish
Season 1: Girls Just Want to Have Fun (Amazon; Black-ish Wiki; Halloween Specials Wiki; Hulu; IMDb)

Modern Family
Season 2: Halloween (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia; Wikipedia)
Season 4: Open House of Horrors (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia; Wikipedia)
Season 6: Halloween 3: AwesomeLand (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia; Wikipedia)
Season 8: Halloween 4: The Revenge of Rod Skyhook (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia; Wikipedia)
Season 9: It's the Great Pumpkin, Phil Dunphy (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia)
Season 10: Good Grief (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia)
Season 11: The Last Halloween (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia)

Monk
Season 4: Mr. Monk Goes Home Again (Amazon; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

Moone Boy
Season 2: Ghost Raft (Hulu; IMDb)

My Little Pony: Friendship is Magic
Season 2: Luna Eclipsed (Amazon; Halloween Specials Wiki; IMDb; TV Tropes; Wikia) Not really about Halloween, but rather a Halloween-like holiday called Nightmare Night.
Season 5: Scare Master (Amazon; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

My So-Called Life
Season 1: Halloween (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; This Was Television)

Ned's Declassified School Survival Guide
Season 3: Halloween/Vampires, Ghosts, Werewolves & Zombies (Amazon; Halloween Specials Wiki; IMDb; Wikia)

The Neighbors
Season 1: Halloween-ween (Amazon; A.V. Club; IMDb; Wikia)
Season 2: Challoweenukah (Amazon; IMDb; Wikia)

Once Upon a Time
Season 2: The Doctor (Amazon; A.V. Club; IMDb; TV Tropes; Wikia; Wikipedia) While not technically a Halloween ep, this aired just a few days before the holiday, and it had a very Halloweenish vibe.
Season 7: Beauty (Amazon; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

Parenthood
Season 2: Orange Alert (Amazon; A.V. Club; IMDb; NBC; Wikia)

Perfect Strangers
Season 4: Aliens (Amazon; IMDb; P.S. Online)

Phil of the Future
Season 1: Halloween (Disney+; Halloween Specials Wiki; IMDb; Wikia)

Phineas & Ferb
Season 1: The Monster of Phineas-n-Ferbenstein (Amazon; Disney+; IMDb; TV Tropes; Wikia; Wikipedia) Not set on Halloween, but it aired near then, and it's Halloweenish.
Season 3: That's the Spirit (Amazon; Disney+; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)
Season 4: Terrifying Tri-State Trilogy of Terror (Disney+; Halloween Specials Wiki; IMDb; TV Tropes; Wikia) Not set on Halloween, but...
Season 4: Druselsteinoween (Disney+; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

The Pretender
Season 2: Back from the Dead Again (Amazon; IMDb; Wikia)

Psych
Season 1: Scary Sherry: Bianca's Toast (Amazon; IMDb; TV Tropes; Wikia) This didn't air around Halloween, and I don't even remember if I saw it or not. But it was mentioned in the 2017 Halloween issue of Entertainment weekly, so I decided to add it here.
Season 6: This Episode Sucks (Amazon; A.V. Club; IMDb; Wikia) I don't remember if this was set around Halloween, but it aired around then, and it's about vampires (sort of), and it had some vampire-related guest stars, including Kristy Swanson, Corey Feldman, maybe some others. So we might as well call it a Halloween episode.
Season 8: A Nightmare on State Street (Amazon; IMDb; Wikia) This definitely wasn't a Halloween episode, but it definitely should have been.

Pucca
Season 1: Them Bones/Ghost of a Kiss/The Usual Ching (Amazon; Halloween Specials Wiki; Wikia)

Pushing Daisies
Season 1: Girth (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

Quantum Leap
Season 3: The Boogieman (IMDb; NBC; Wikia). I think this was the first episode I ever saw of the series, as I didn't get NBC and my local CBS station only started airing the show, as far as I know, with the third season... possibly repeats, because this originally aired in October 1990, but I kind of feel like I saw it in the summer. I could be wrong, though.

The Real O'Neals
Season 2: The Real Halloween (Amazon; Halloween Specials Wiki; IMDb; Wikia)

Reaper
Season 1: Leon (Amazon; A.V. Club; IMDb; Wikia)

Rock Lee & His Ninja Pals
Season 1: Deidara's Art is Always a Blast! (Halloween Specials Wiki; Hulu; IMDb; Wikia)

Roseanne
Seasons 2-9: Roseanne: Tricks & Treats

Sabrina the Teenage Witch
Season 1: A Halloween Story (Amazon; Halloween Specials Wiki; Hulu; IMDb; Paramount+; Wikia)
Season 2: A River of Candy Corn Runs Through It (Amazon; Halloween Specials Wiki; Hulu; IMDb; Paramount+; Wikia)

Saturday Night Live
I don't exactly know of any single episode that was specifically for Halloween, but there have, over the years, been many episodes that contained Halloween sketches. The ones I'd know would be from the 90s, but I'm sure they started doing such things in the 70s, and still do them now. And occasionally they might air a compilation episode of such sketches from over the years.

Scream Queens
Season 1: Pumpkin Patch (Amazon; A.V. Club; IMDb; Wikia; Wikipedia)
(This is sort of a two-parter; the previous ep, "Haunted House," introduced the holiday "Chaneloween." According to Wikipedia, the next episode is also part of a Halloween three-parter, but I don't recall the next episode being involved with Halloween, so I'm not sure. In any event, I think the middle episode was the one most definitely set on Halloween.)
Season 2: Halloween Blues (Amazon; IMDb; Wikia)

The Secret Circle
Season 1: Masked (A.V. Club; IMDb; Wikia; Wikipedia)

The Secret World of Alex Mack
Season 2: The Secret (Amazon; IMDb)

The Simpsons
Seasons 2 - present: Treehouse of Horror
Season 27: Halloween of Horror (Amazon; A.V. Club; Disney+; Halloween Specials Wiki; IMDb; Wikia; Wikipedia)
Season 34: Not It (Amazon; IMDb; Wikia) A parody of IT

Single Parents
Season 1: Politician, Freemason, Scientist, Humorist and Diplomat, Ben Franklin (Amazon; Halloween Specials Wiki; Hulu; IMDb; Wikia)
Season 2: Welcome to Hell, Sickos! (Amazon; Halloween Specials Wiki; Hulu; IMDb; Wikia) Note: this episode has an escape room

Sleepy Hollow
Season 3: Dead Men Tell No Tales (Amazon; A.V. Club; IMDb)

The Smurfs
Season 3: All Hallows' Eve (Amazon; Halloween Specials.net; Halloween Specials Wiki; IMDb; Wikia)

So Weird
Season 2: Boo (Disney+; Halloween Specials Wiki; IMDb; This Was Television; Wikia)

South Park
The series has done several Halloween eps, but right now these are the only ones I remember.
Season 1: Pinkeye (Amazon; A.V. Club; Halloween Specials Wiki; Hulu; IMDb; TV Tropes; Wikia; Wikipedia)
Season 16: A Nightmare on Face Time (Amazon; A.V. Club; Halloween Specials Wiki; Hulu; IMDb; TV Tropes; Wikia; Wikipedia)

The Spectacular Spider-Man
Season 1: The Uncertainty Principle (Amazon; Halloween Specials Wiki; IMDb; MAU Wiki; TV Tropes; Wikipedia)

Speechless
Season 1: H-a-l-- Halloween (Amazon; Halloween Specials Wiki; IMDb; Wikia)
Season 2: N-i-- Nightmares on D-i--Dimeo S-Street (Amazon; Halloween Specials Wiki; IMDb; Wikia)
Season 3: I-n-- Into the W-o-- Woods (Amazon; Halloween Specials Wiki; IMDb; Wikia)

Suburgatory
Season 1: Halloween (Amazon; A.V. Club; Halloween Specials Wiki; IMDb; Wikia)
Season 2: The Witch of East Chatswin (Amazon; A.V. Club; IMDb; Wikia)

Sunnyside
Season 1: Skirt-Skirt! (Amazon; Hulu; IMDb; Wikia)

Supernatural
Season 4: It's the Great Pumpkin, Sam Winchester (Amazon; Halloween Specials Wiki; IMDb; TV Tropes; Wikia)

Totally Spies!
Season 3: Halloween (Amazon; Halloween Specials Wiki; IMDb; Wikia)

The Troop
Season 1: The Great Punkin (Amazon; IMDb; Wikia)

Veronica Mars
Season 3: President Evil (Amazon; A.V. Club; IMDb; TV Tropes; Wikia)

Video Hits
I'm sure at least one year in the late 80s or early 90s, this show had an episode with Halloween-themed videos, like Michael Jackson's "Thriller" and Harry Belafonte's "Day-O" (from Beetlejuice), but I don't recall what else it included.

The Weekenders
Season 4: Nevermore (Halloween Specials Wiki; Wikia)

W.I.T.C.H.
Season 2: W is for Witch (Halloween Specials Wiki; IMDb; Wikia) This episode originally aired out of sequence in order to be watched shortly before Halloween. I did not watch it until later; the network scheduling decision seriously pissed me off, because the series is serial in nature, not episodic... and also, every episode of season 2 had a title specifically starting with a letter of the alphabet, so it should be obvious in what order the episodes should air, dammit.

Zeke and Luther
Season 1: Haunted Board (IMDb; Wikia)