- “It’s a Good Life”. Twilight Zone
- “Lonely Souls”. Twin Peaks
- “The Zombie” Kolchak:The Night Stalker
The pilot for the Night Gallery series – Rod Serling’s followon to The Twilight Zone – contains three different stories that IMHO are contenders for this category. But my favourite by far, Escape Route, concerns a Nazi war criminal hiding out in Argentina. He is a frequent visitor to an art gallery where he is strongly attracted to a peaceful painting of an old man fishing from a rowboat. In his quest for serenity, he finds that by concentrating deeply he can, by sheer power of will, enter the painting and become that old man. Later, pursued by Israeli agents, he uses that uncanny power once again, only to find himself facing a horrible retribution.
The original Outer Limits show had plenty of worthy contenders for top horror episodes.
The Zanti Misfits will certainly quicken your pulse and make you quake with fear:
Night Gallery: The Caterpillar is why I always pull the covers over my ears.
Actually, I was going to mention that one. Besides the three great stories in the pilot that I mentioned, The Caterpillar is very memorable, in a horrific sort of way! The pilot and the episode with that story are part of my small Night Gallery collection.
Part 3 of “Trilogy of Terror”, with the Zuni fetish doll, has gotta be right up there.
Aw, the Zanti Misfits would eat the Zuni fetish dolls for lunch! 
The pilot episode (“Days Gone Bye”) of The Walking Dead is my favorite, followed by the opening Night Gallery pilot story “The Cemetery.” Third place goes to the Night Gallery sequence where Leslie Nielsen overnights in a haunted house on a bet and loses big time. [Beware! Some runs of NG are half hour episodes and the Nielsen story will make no sense as 10 to 15 minutes are cut for commercials.]
Honorable mention: The Outer Limits Martian(?) sand shark epi with Adam West.
The Bent-Neck Lady - You will need to watch the four previous episodes of Haunting of Hill House, but this episode is an all-time great.
Imprint - This was an episode so horrific, Showtime refused to show it on their show Masters of Horror. I was able to stream it on Hoopla, the library streaming network. Yeah…that was kind of insane.
Home - This is the X-files episode that everyone remembers as “the one Fox didn’t re-air in syndication”. It’s horrific, but one of the very odd things is that when you watch it, it actually contains an odd level of humor, almost out-of-place for how messed up the overall episode is. A great X-files, though.
“Nightcrawlers” from The New Twilight Zone, especially in its original airing, with no commercials.
“Specimen: Unknown” from The Outer Limits
Talking Tina (Living Doll).
^ Doll Repairman: Yep. Here’s your problem. Someone set this thing to “evil.”
The insane cuts to NG is why i bought it on DVD…same for Night Stalker. Well I havent bought them yet, but I will.
Nice call. I might have added that to my list and replaced two or three, had I remembered it.
There’s some kids horror my children were watching, Goosebumps or such…the episode is about a school mascot that is actually the monster it pretends to be. At the end, the middle school protagonist tries calling his two buddies, and a ringing can be heard coming from the stomach of the creature where a cutaway reveals the two children screaming in its stomach.
I ran scrambling to find out what happened in part two but there was no part two. That was it. I was stunned.
Night Gallery’s “Pickman’s Model”.
Lotta love for Night Gallery in these parts. There’s a very short episode, like 10 minutes featuring Diane Keaton who is manipulated into murdering her BF in jealousy. She’s a delight. Just being her normal frantic Diane Keaton self.
Buffy the Vampire Slayer: Hush
Buffy the Vampire Slayer: Ted
The X-Files: Squeeze
Beware, Part II: some NG video collections omit an episode with Ruth Buzzi and some other ladies as a witches’ coven and I have no idea why.
Beware, Part III: Some NG TV runs jam in episodes of Tales of the Unexpected to boost the number of eps to 100 for syndication purposes.
This thread made me pull up the pilot on YouTube just to hear Roddy McDowall yelling for Portefoy. And later, Portefoy screaming at Jeremy to get back in the ground where he belongs. I love it!
There’s a series on Hulu called Bite Size Hallowe’en that features short horror films. Worth a look, once.
Twilight Zone - “The Howling Man”
Somebody already mentioned my other choices.
Alfred Hitchcock Hour - “The Jar”.