1/0 had "Max's World", a short comic created by Max to illustrate to Marcus what a comic strip is. Since the strip itself (1/0) is about metaphysical issues and the nature of reality, the comic strip characters creating a comic strip may also be an example of Recursive Reality. "Max's World" doesn't last long, though, since the 1/0 characters get jealous of the girlfriend Max drew for his main character and squash him with an anvil in the next panel.
In the beginning, Ansem Retort was mostly focused on its status as a webcomic about a reality show filled with jerkasses and cloudcuckoolanders who were all addicted to at least 3 illegal drugs each. Cerebus Syndrome has kicked in a bit as the series goes on and things get more serious (well, as serious as that freak show gets, anyway), but they still bring up things like ratings, and in fact often let events occur because they wouldn't have a plot for the next season otherwise.
In Archipelago, Kor (a professional actor and a master of Flynning) is introduced on stage, playing an important part in "Cord of Gold". He later quotes from it during his (real) duel with The Heavy.
Kor: So let me get this straight - you have what I want, and I have what you need.
In Arthur, King of Time and Space, Arthur and Merlin both have webcomics (Merlin's is later taken over by Nimue). Arthur's is a Life Embellished strip called The Thing of Shapes to Come and Merlin's is about aliens and called The Land of Whant. There was a crossover, in which the aliens came to Earth and befriended Arthur.
Much of the early plots of DDG centred on the afterlife gameshow You Bet and Zip's (reluctant) employment as Ms. Fanservice.
Dont Look It Sucks features Star Dork a fictional Sci-Fi series enjoyed by some of the comic's cast.
In El Goonish Shive, Elliot and Susan have a small online movie review show that has achieved some small local popularity. It has spawned a number of In-Universe Elliot/Susan shippers.
In Faux Pas, Myrtle, Shipper on Deck, retells Tarzan with Randy as the ape-fox and Cindy as the intrepid archeologist.
In Gifts of Wandering Ice Rikter proudly admits that he knows eight legends about the ice gifts, several of which he tells to the Cave Dweller teens at the beginning of the story.
While on the run from the Baron in Girl Genius Agatha joins a circus which is also a traveling Heterodyne show and ends up playing the exaggerated version of her mother the plays feature on multiple occasions.
The interlude City Face is implied by The Rant and the Shout Box (which portray the City Face characters as Animated Actors) to be a fictional film. Its only connection to the Gunnerverse (apart from Word of God saying that City Face is Canon) is that the actors include Zimmy, Gamma and City Face, the pigeon Kat rescued.
Dr Disaster's Virtual Training Simulations have a stronger connection to the plot as they are played by the students of Gunnerkrigg Court.
While Zoe is stuck in a time-dilation hero-ing situation in Heroine Chic, her fashion studio's lease expires. Her former boss Dyna Cuff buys the lease out from under her and moves in. The renovations to the space get a six-episode HGTV special called "Dyna Might."
Homestuck features several. The most prominent is Sweet Bro and Hella Jeff, a Stylistic Suck parody of Two Gamers on a Couch webcomics ostensibly made by Dave Strider; most of the cast often quote it to each other, and segments of it sometimes show up in the narration as part of Homestuck's love of the Meaningful Echo. The three previous MS Paint Adventures series also exist, both as comics and as videogames, as well as a fictional fourth adventure about the Midnight Crew. In the Midnight Crew universe, which is really in the far future of the troll universe, Homestuck exists on MS Paint Adventures. Also present are Squiddles!, a Sickeningly Sweet television series which is actually mankind's subconscious representation of certain Eldritch Abominations; Game Bro, a Straw Critic gaming magazine; Grand Snack Fuckyeah, a invokedthoroughly broken skateboarding game/Product Placement bonanza; and Complacency of the Learned, a wizard story Rose is writing and appears in the post-Scratch Earth as a series. Wizardy Herbert (a fanfic about the Post-scratch version of Complacency written by Roxy) also makes a brief appearance.
In Kevin & Kell, Rudy creates two webcomics. The first is about human versions of himself and Fiona called Rhondo and Viola and the second is about a sheep and called Mad About Ewe.
Last Res0rt features the reality show of the same name, crossing Survivor with Battle Royale and inadvertently setting up a plot that resembles Professional Wrestling moreso than anything else.
Billy Thatcher of morphE is the star of a reality TV show named Pawnography. The show is presently on hiatus due to its star being kidnapped by a flirtatious young mage with blonde curls and an affinity for chess playing reality TV show stars. One of the characters is only aware of Thatcher and his show due an in-universe 4Chan meme using sound-bytes from the show.
My Impossible Soulmate: This one gets a bit meta. My Impossible Soulmate is a stand-alone prequel to Rain (2010) which largely takes place in the High Fantasy world of Rain Flaherty's favorite Manga, Black Wings: Kaminari. So MISInverts the trope because instead of having a show within a show, it literally is the show within a show. But it goes even deeper than that. The main character of MIS is a Japanese high school girl named Chiaki Koizumi who gets Isekai'd into Kaminari's world and, later on, returns home to write and draw Rain's favorite manga. This implies pretty strongly that Koizumi's manga that Rain loves so much isn't the fictional Fantasy story it appears to be, but rather, is a historical Documentary about another world in an Alternate Dimension.
In Nine to Nine the author's other webcomic, Swords and Sausages, exists as a web video series made by secondary characters Tor and Andrea.
Nip and Tuck has "Purloined Letters Productions", a shoestring B-movie/direct-to-video company that has, to date, produced such epic hits as Man on the Border, Rebel Cry, 10,000 Ninjas, Gravedigger, and Scurvy Dogs: The Curse of Blackbeard's Treasure.
A Tale of Fiction features "Bison and the Boar Boys", a comic with no bearing at all to the main plot (as of yet) and no connection to the characters, but which can nevertheless be accessed from one of the characters' laptops ("dragbook"). Also available on the dragbook is an in-universe blog called "I Am Not Fiction". Only Bison and the Boar Boys is regularly updated as of now, although I Am Not Fiction is likely to soon follow suit.
Zombie Ranch is not only the name of the comic but the name of the in-universe Reality TV Show being filmed about the characters' lives. The comic occasionally cuts between the "live" recordings and what seem to be more produced segments being aired sometime in the future.
Characters are fans
Okay, little bit of an odd example. Ansem Retort is a webcomic about a reality show. Darth Maul, one of the cast members, likes to watch said show. Yes, this includes watching himself watch the show.
Darth Maul: That's some paradoxical shit right there!
In Cucumber Quest: The TV Show Punisher Pumice. Little is shown about it, but we know that Almond is a Fangirl. Almond also says in a Q&A that she learned sword fighting by watching TV, "especially from Punisher Pumice" . Peridot is a pretty big fan of the series as well. The current season got political in-universe by including a plot about the Disaster Masters, the cast goes to the Crystal Kingdom, where the series is made, and Cucumber mixed up his wand with one of the show's props, and Bacon turns out to be cast in the role of Pumice's best friend Pancetta.
In Dumbing of Age, Walky, Dorothy, and Ethan are fans of the cartoon "Dexter the Head Alien and the Monkey Master",. Both the Head Alien and Monkey Master are characters of another comic by the same author. Carla is a fan of the Ultra Car cartoon, Ultra Car's gynoid chassis in Shortpacked! being the genesis of Carla. Ethan eventually gets Joyce to become a fan. A reoccurring story arc in the second semester is Joyce creating Roommates!!!, the precursor to her story about Julia Gray, Space Pilot (and a big reminder that Joyce is David Willis's Author Avatar).
In the webcomic El Goonish Shive, some characters are fans of the Lucky Bunny Bounty Show (which was canceled after only 22 episodes).
Ennui GO! has The Jimmies, a kid-oriented cartoon and puppet variety show Max and his friends watch that is entirely inappropriate for kids. It usually pops up whenever the author wants to comment on modern-day kids shows.
The titular character of Erma loves a show called Warrior Princess Unicorn. It's advertised as being a princess-centric kid show, but it's actually an action-packed drama, which surprises Erma's babysitter when she sees it for the first time.
Multiple Girl Genius characters are fans of the Heterodyne stories and plays, which are based on Agatha's parents and uncle even if a lot of the material is made up whole sale or incredibly otherwise off when compared to the reality of their lives.
Gil is a huge fan of the Trelawney Thorpe novels.
The (extra content) radio plays are apparently very popular in some places, but not with Agatha who turns up to the end of every episode with a missile launcher or death ray.
Girly features Action Up The Butt, which is what happens when you take the concept of Highlander (where killing someone gives you their power), make all the characters 19th century authors (with Sir Walter Scott as the main character), then give them all guns. It was cancelled after the second season.
Mark Twain: So, you've heard those rumours about me, have you? Sir Walter Scott: I... I didn't want to believe them... but... Mark Twain: That's always been your problem, Sir Walter Scott. You never wanted to believe anything. And now, there will be rumours about you. Specifically, your death. And they will NOT be exaggerated!
In Heart Core, it is shown that Ame is really into the cartoon show called Royal Jelly Complex. Most of it has to do with that she is easily distracted by video entertainment.
Leif & Thorn features a bunch, mostly sequences from from Hedge & Grassie, a sitcom Thorn is a fan of. Other referenced properties include Leachtric (musical), The Holger Saga (literature), Pretty Combat Mountaineer Geirskögul and Magical Storm Rune Svanhvit (magical-girl comics).
My Life at War: Vulture is a fan of a show about a mercenary mecha pilot called The Southpaw.
Erik and Oriel are briefly shown at the beginning of Chapter IX watching and enjoying The Duchess of Apalthi, a play by the World Oak's greatest genius playwright, Oskar Webster. All we get of it is the ending where the duchess renounces all company for the rest of her life.
The Gnome President is briefly shown watching a scene from that same playwright's Courtroom Madness, which is apparently a dramatisation of a trial of the World Oak's greatest criminal, Zeta Toad. Given the brief idiotic giggle he gives as he watches it, it's clear he's enjoying it.
Another play entitled Olly Jickle Clock Sits In the Stocks And Gets Pelted With Burning Koals is also shown to exist as shown by a poster in Chapter V, and in Chapter XIX there is a poster for a play entitled The Foul Murder of Stupid Bloudy Johnson and His Inordinately Obeze Wyfe.
Questionable Content: Marigold and Hannelore are fans of the manga/anime Magical Love Gentleman.
Rain (2010) has at least three separate show-in-show anime/manga series that were created for the comic. They can be a bit hard to pick out, as the comic artist is very fond of Bland-Name Products, so she frequently mentions real anime/manga under changed names (example: the characters watched Hardsteel Physicist rather than Full Metal Alchemist). But she mentions the originals in The Rant when they come up.
Halloween Princess Pandora is a dark and violent Magical Girl anime, of which Maria is a huge fan. She has a cosplay outfit of the main character that she made herself, and she wore it as her costume during Emily's Halloween party.
Also, there is Mad GigaKaizer X, a giant mecha anime along the same lines as Gundam. Gavin likes it so much that he collects figurines of the robots.
Of course, of the three originals, the comic gives the most attention to Rain Flaherty's favorite, Black Wings: Kaminari. After all, Rain is the titular character, and she is more than happy to get her friends as hooked on it as she is. It is a High Fantasy adventure manga, and serves as a rather unsubtle metaphor for Rain's challenges as a trans girl.
Chapter 25 of the comic is a long dream sequence where Rain envisions herself and her friends as the character Kaminari and her friends.
There is now a stand-alone prequel comic, My Impossible Soulmate, which is largely set in the fantasy world of Black Wings: Kaminari.
Devious Gingers on BBC 42 is James' favorite show in Roommates.
Selkie has The Adventures of Sue and Kathryn, characters from one of the author's previous comics. They are a ten-year-old zombie and wraith, respectively.
Bobbinsverse: Steeple features Clotted Crime, a Sunday evening TV mystery series with a bit of a Cozy Mystery aspect and similarities to Midsomer Murders but set in Cornwall. Mrs Clovis and, more surprisingly, Maggie are big fans; Reverend Penrose despises it, calling it “churchsploitation”, because any vicars who appear in it are milksops or murderers, or both. After a hurricane devastates every other village in Cornwall, the production comes to Tredregyn to shoot some episodes.
Type 1: Joanna has written and published a successful trilogy of young-adult fiction books called "The Rain Children." The launch party of her 3rd book is held in Bell Corner Bookshop (which is run by Walt's parents) and Lucy is put in charge of planning the event by Mrs. Smith.
Type 2: Lucy, Joanna, and Walt are all fans of a TV show called "Detective Mystic" about a supernaturally-empowered detective investigating the murder of her husband. They're very invested in the love triangle between the titular detective, her current partner on the force, and the private investigator who is an old friend. (Joanna ships Detective Mystic and her partner, Walt ships Detective Mystic and her old friend, while Lucy wants all three to end up in a polyamorous relationship.)
Type 2: Several cat characters and Peanut are fans of the book series Pridelands, seemingly a Warrior Cats/The Lion King (1994) spoof. Verges into Type 1 when the author of the series becomes a recurring character.
After The Curtain Call: The two main characters are actress and theatre fan, so the story is bound to have both.
Type 1: The actors and producers in the story take part in plays, mainly the following four: Macbeth, Paule et Roger, Romeo and Juliet, and Ophelia.
Type 2: Soyoung, one of the two female leads, is a theatre nerd. She only watched musicals at first, but after watching Jaeyi on the stage, she has become a big fan and goes to almost every shows of Jaeyi.
Stylistic Suck included.