To start us off:
Where: Friday the 13th: The Series.
Comic: Tales of the Undead.
Creator: Jay Star.
Publisher: Peerless Comics.

Tales of the Undead featured the adventures of the robotic (or maybe cybernetic) Ferrus the Invincible. In Friday the 13th: The Series, the show's concept was that a warlock had cursed various items for the Devil, then sold them from his pawn shop; now the warlock was dead, his heirs were seeking to retrieve the items and stop them causing death and mayhem. One of the cursed items was a rare first issue of Tales of the Undead, which could transform people into a murderous version of Ferrus. The transformation sequence saw the user first assume an "illustrated" appearance:

before then becoming "real world."

Where: Hustle (TV series)
Comic: Black Storm
Creator: Leonard Wright
The British TV series Hustle was about a team of grifters (con artists), and in the second season episode Missions they decided to trick an investor buying a forged copy of the cover artwork for the first issue. Per the episode, Black Storm was one of the original superheroes, published in 1934, and the first issue was considered the "Mona Lisa of comic book artwork." They bought a genuine copy at auction, used it to fool the auction house's authenticators when they resold it for even more, but switched the art and gave the investor buyer the forgery, while reselling the real artwork to a genuine fan at a high, but more reasonable, price.

Okay, separating things out. From the start of my original post:
I couldn't find an images of the comic (if there were any) but Fantasy Island season 3 episode 23 "Eagleman/Children of Mentu" May 17, 1980 referenced an Eagleman comic book.


 

Last edited by Andy E. Nystrom (8/08/2020 5:47 am)

Where: Hustle (again)
Comic: Warrior Women / Wild Avenger

Same episode as above. Less info about these issues, as they were hidden among genuine comics in a scene set in a comic shop. The fake titles were used for two reasons: firstly, because they were the issues we saw in close-up, and second, because they needed comic covers with oversexualised women, so the female con artist could sigh and comment how "sad" they were. Unfortunately, while an otherwise enjoyable episode, the writer did feel the need to play all the standard negative stereotypes about comics and comic readers - the comic shop owner who was one of the potential buyers for the art is portrayed as a socially inept geek who is clueless around women (and yes, I know there are fans like that, but it'd be nice not to have movies and TV portray EVERY fan like that). 

Throughout Watchmen (original limited series 1986-1987), Bernie (the kid at the newsstand) reads a Tales of the Black Freighter comic story Marooned written by Max Shea and drawn by Walt Feinberg.

Where: The Chronicle (TV series)
Comic: Captain Vigilant

In the short lived series The Chronicle, about a tabloid reporting on genuine supernatural events, the 16th episode Man and Superman featured them investigating what appeared to be a real-life superhero. They eventually discovered that their hero was actually a telekinetic comic fan reproducing events from the comic Captain Vigilant, a title that had been popular in the 1980s until the crash in the comic industry killed it. It ran for at least 23 issues, as the show's resident comic book fan (for once not portrayed as a socially inept loser, and clearly written by someone who genuinely knew comics, given some of the references he dropped) mentions events that happened in "Captain Vigilant#23." We only get a glimpse of the comic cover, and a little more of the interiors.

An interesting subcategory is comics that eventually existed:





 

Where: Condorman
Comics: Condorman, Laser Lady, Zowie Comics
Creator: Woodrow Wilkins
Publisher: Woodrow Wilkins Publications.
No image of the Condorman comic itself, though there are copies of "Woodrow's" design sketches:


and there are images of the other two comics, plus some interior pages of Laser Lady:

Where: Utopia
Comics: The Utopia Experiments
Creator: ?
Publisher: ?

The British TV series Utopia featured a fictional graphic novel series, The Utopia Experiments, as the catalyst for the entire story.

In the series, they deliberately only showed random pages, such as these which had been ripped out and pinned to a wall:
and these, held by a character:

Here's a better shot of one of those pages:

However, to promote the DVD release, they did an actual version of the graphic novel as a limited edition item:

Where: Crash - Truslen fra det sorte hul
Comics: Thunderbot
Creator: ?
Publisher: ?

The 1984 Danish series Crash - Truslen fra det sorte hul ("Crash - The Menace from the Black Hole") featured the comic Thunderboy, which was stolen from series protagonist Birger by the supervillain Barry Slisk. 

Loki wrote:

Where: The Lost Boys
Comic: Destroy All Vampires / Vampires Everywhere



Fake vampire comics created as props for the 1980s movie The Lost Boys, which from the covers are some what "Tomb of Dracula"-esque. Unlike the other comics mention, you CAN buy these though! A few years ago someone got the rights and produced facsimiles of the props, complete with interior stories that obviously weren't shown in the movie (not sure if they props had interior stories or not, and so unsure whether the facsimiles made up a new story or reproduced unseen material that was actually made for the movie - but I suspect the former). And these facsimiles are available to purchase.
 

And Blackthorne Publishing and their book XL (seen on the back cover) are real

Great additions Sidney!

comics that eventually existed:

Where: Jingle All The Way (movie)
Comic: Turbo Man
Creator: ?
Company: Exciting Comics

In the movie Jingle All The Way, Turbo Man is a TV superhero and hot Christmas toy. But he's also in a comic!

Where: Zoom: Academy for Superheroes (movie)
Comics: Zoom
Creator: ?
Company: Pow Comics, Revolution Comics

The movie Zoom (based on a comic, but the comics depicted below are not those) featured a retired hero by that name, who in his time had enjoyed licensed comics. Thus both in the movie and as part of an epilogue montage, we saw various examples of said comics.