Destroy the Godmodder: Very common. The main idea behind it is that it takes place in a video game (Minecraft specifically, although so heavily modded as to be completely unrecognizable) and many of the characters know that. Even canonically fictional ones. In the second game, the actual Fourth Wall of Minecraftia is broken, causing the Homestuck Invasion
Bioshock: Above the Sea: Zero does this twice, once, when a roleplayer states her upset at being dumped Zero "kills" her ex in the actual roleplay, and another time when he spends a few seconds speaking with the roleplayer that made him.
This was a prominent running gag in We Are Our Avatars, where characters like Bass, Deadpool, Bernkastel, "Raven", among others, would refer to the readers and the people reading, but, the gag was done to death and it's since been downplayed. It got to the point where Etheru retconned the ability out of Bass because of annoyance with the gag.
In the Cold Opening to episode 5, Boat is attempting to speak French with Baguette using the dictionary he purchased in a previous episode. Once Boat asked Baguette to repeat what he had just said, Baguette asked Boat if he couldn't see the subtitles. At which point the subtitles themselves address Boat. After witnessing Baguette getting hugged by the subtitles, Boat proceeds to break a wall labelled 4.
Becomes a Brick Joke in The Stinger. When Boom Box mentions how some of the characters there (him, Party Hat and Shieldy) were recommended characters and Party Hat agrees (while looking at the screen to boot), Boat once again breaks the same wall.
Nora: Nope! Never happened! Everything's FINE! Pyrrha. Is. FINE! And nothing bad. Ever. Happened. (Turns to face the viewer.)EVERRRR...
Episode 23 goes completely and utterly nuts with this trope as Nora downs an entire pot of coffee and ends up travelling through various dimensions she ends up in the real world. She's brought back to "relative" normal when her voice actress drinks coffee.
EVTV Weather has a few occasional 4th wall breaks. Along with the character of Maggot Man, who serves as a pseudo-narrator.
In sooper appisote 3, the entire series font gets changed midway through the sooper appisote, due to someone pressing a button that said "CHANGE FONT".
And in A.18, Liteslayer and Deine indirectly break the fourth wall by acknowledging the live evolution happening to them. It starts by a text-to-speech-translator, getting colored, then spelling properly, then so on and so forth until Lite kills himself to stop any more "evolution" from happening.
The fourth wall is broken continuously in the Alfred's Playhouse series. Alfred address the audience as "boys and girls" and in the movie, Dictator Pickles personally introduces Alfred to the audience.
Homestar Runner does this, particularly in the "Virus" Strong Bad e-mail where the format of the web page gets tampered with. Also, "My mouth was a broken JPEG!" Happens literally in some of the iTunes openings, where Strong Bad will either press his face against the screen, leaving a print, or literally try to break your screen!
At one point in a Happy Tree Friends interactive minigame, a character is killed when they're crushed against the fourth wall.
KateModern comes dangerously close to breaking the fourth wall on a number of occasions, always with some in-universe justification (however flimsy). They finally break it directly in "The Last Work", when Tez, after talking to an off-screen Meryl, turns to the camera and says, "She should get her own show, that one." This was also a direct Shout-Out to the fanbase, as the concept of a Spin-Off called "MerylModern" was a popular fan in-joke. Of course, KateModern never had a Fourth Wall in the traditional sense, because while the characters aren't aware that they are fictional, they are always aware of the audience and address them frequently. The fictional "fan" Sophie, in particular, broke the fourth wall repeatedly on her Bebo profile.
In The Guild, Codex breaks the fourth wall at the start of every episode, talking to the audience about what's bothering her.
There is a bit of fourth wall breaking in The Cartoon Man saga. While no one ever acknowledges their existence as characters in a movie, Roy looks into the camera numerous times as if acknowledging an audience. It's played as one more aspect of acting like a cartoon character. Roy and Valerie also go through a "montage" in the third movie, and specifically refer to it as such.
Left POOR Dead: Frequently, examples include Dr. Smedly refering to himself as the antagonist and Tippy knowing Toby's name from seeing it in the opening credits
In I'm a Marvel... and I'm a DC almost every character knows that they are comic book characters and they frequently meet at the hero bar "Stan's Place" to talk about the movies and tv shows that are based on them. However, Deadpool still manages to be one step ahead of everyone else by being the only character to know that they are all action figures in a Youtube video series with long waiting periods between videos.
Pretty much the only character to not know about his comic origins at first and believe himself to be real is Darkseid. Once he learns the truth from Joker, he admits it was a blow to ego but then he takes the time to study his comic origins and Marvel's, learning about the writers, artists, and continuity, until he uses the concept of reboots for his next Evil Plan. He is thwarted when Deadpool uses his own device against him to transfer his knowledge of their world into Darkseid's head, and Darkseid, has a breakdown, being unable to handle that he is really just a toy.
Any article with the Pataphysics tag ("Pata" being the step above "Meta") deals with the fictional nature of the Foundation, such as the Foundation realizing it's fictional and trying to influence the writers or readers or even the wiki itself.
The chapter Super VisionLampshades this when Johnny Dark cautions Maria not to overthink the nature of the Sands, because it makes the author irritable. Later, Tigerlily Bender seems to fall afoul of this same phenomenon.
In the Whateley Universe, the Monkey King is a godlike being who apparently has this as a power. In his own point of view short story, he repeatedly addresses the readers and even makes comments about some of the forum posters.
In one of the Soul Pancake video "Unexpected Visitor" the intruder tells the guy, and atheist he is God, the guy says "you just lost me" to which God says "that's okay, we probably just lost about Half our audience." then looks and winks at the camera.
The Last Generation runs over the fourth wall with a bulldozer and then pees on its remains. After hopping through several worlds across the Multiverse Inna, the main character finally reaches our own, where she meets her creator, who proceeds to explain that she's just a character in a roleplaying forum whose uniqueness is the result of several retcons, and the reason her world is being destroyed is that the forum has closed down due to inactivity.