A Midsummer Night's Dream deserves special mention for Puck's ending speech, which can be condensed into "We're sorry if you didn't like the play," and, essentially, a Shakespearean version of the MST3K Mantra.
Even before that, Oberon seems to be addressing the audience when he explains how he is Invisible to Normals.
It also deserves a secondary mention for the continuous breaking of the fourth (fifth?) wall in the Pyramus and Thisbe sequence. Frequently the action stops so Bottom can reply to the characters watching the play. Plus the prologues. Oh, the prologues.
And of course in Henry V where the opening monologue is an extended apologia for not showing the tremendous battles that are going on in-between the play's scenes. Made doubly strange because it was retained in both the Olivier and Branaugh films of the play, where they do show the battles.
Any time Iago opens his mouth he is likely to address the audience by the end of the speech.
One of Hamlet's many soliloquies (this one in Act II, scene ii) includes the lines "I have heard that guilty creatures sitting at a play/Have by the very cunning of the scene/Been struck so to the soul that presently/They have proclaimed their malefactions..." A great many productions have Hamlet break the fourth wall at this line and speak directly to the audience, for a darkly comedic effect.
Bertold Brecht was famous for this, or as he called it: the Verfremdungseffekt. He largely used it to draw attention to important elements.
One particular scene early on in The Pirates of Penzance when the Pirate King swings out into the audience during a song, and ends up getting into a sword fight with the conductor of the orchestra.
The Narrator of Our Town doesn't so much break the fourth wall as completely ignore it. The rest of the cast is entirely unaware that they're in a play or that what's happening isn't real, but the Narrator talks to the audience throughout the entire show. In between narration, he inserts himself into the action by picking up different bit parts, such as the owner of the soda shop, and interacting with the characters as one of them.
A more subtle but no less important one appears in the second act when during the wedding of two of the characters, the bible that the minister (also played by the Narrator) uses is not actually a bible but is in fact a copy of the screenplay.
Normal in pantomime, and many other forms of audience participation theatre.
Subverted in plays like Moby-Dick Rehearsed where the action is set on the stage of a theatre and the front few rows are kept empty so that the cast can use them as though they were in an empty theatre.
Not to mention plays that remove the fourth wall altogether and have the actors go out and bother the audience.
Or even just move through them (or out from amongst them).
In RENT, Maureen asks the audience to moo with her near the end of her protest. Prior to that, during her first entrance, she asks "which way is the stage?".
In [title of show] during a blackout in a scene where Susan isn't supposed to hear Jeff's dialogue, she calls him out for eating her turkey burger.
Hunter reads aloud a real online post as a revenge of sorts, "Dear Talkin' Broadway's 'All That Chat,' is it true [title of show] has its eye on Broadway? Why would anyone think a tiny, 'insidery' downtown show would appeal to a wider audience is beyond me. I'm sorry, but four chairs and a keyboard do not a musical make. That said, I wouldn't be surprised if their crappy show actually does get to Broadway and they just put this entire posting in it word for word. Signed, sweeneyluvr12."
Done all throughout N F Simpson's A Resounding Tinkle. At numerous points, the 'Author' comes on to explain to the audience about what is happening; characters discuss whether they should carry on entertaining the audience or just leave them to it, at one point a group of critics come on stage and discuss the play so far and the play ends when an audience member protests loudly about the quality of the show.
Smashed to ribbons in Spamalot when the Lady of the Lake explains to Arthur that he is in fact in a Broadway/West End Musical, and they go out into the audience to look for the Grail, which is found under a patron's chair.
And while the Lady of the Lake's actor interrupting the show with a song complaining about being part of this absurd show where the characters are looking for shubbery and she needs a better agent isn't technically Breaking the Fourth Wall, because she's playing herself, after she does get back in character she make a comment about the fact she hasn't been on stage for far too long, although she had a great lounge number in act 1. Which is strangely meta, because the actor has been on stage, in the aforementioned interrupting song, but the character hasn't.
Used for both humorous and chilling effect in the Stephen Sondheim musical The Frogs.
The humorous: The opening song, "Invocation and Instructions to the Audience":
"When we are waxing humorous,
Please don't wane.
The jokes are obscure, but numerous —
The chilling: The god Dionysos has gone to the underworld to retrieve a great dead playwright whose new work can revitalise the public and save the world, but Pluto, king of the underworld, discourages him, and a chorus of the dead counsels inaction and apathy:
"And a leader's useful to curse,
And the state of things could be worse.
It's only a play."
This is directly from the original. Aristophanes' ancient Greek comedy, Frogs, opens with Dionysus' servant Xanthius asking (per the Paul Roche translation), "Hey, boss, like me to perk things up a bit with one of those corny cracks that always get the audience laughing?"
Aristophanes believed that the fourth wall existed to be broken. Clouds has the Anthropomorphic Personification of the right and wrong arguments arguing about stoicism. The right argument voices the opinion that if you're hedonistic your landlord will think you're gay. The wrong argument then defeats this by pointing out that most politicians are gay, most religious leaders and from the look of it most of the audience too.
In The Wasps, Aristophanes had one guard start to indulge in some As You Know about what they are guarding; the other guard is annoyed because they both know it; and the first guard points out that I know and you know but do they — indicating the audience — know it?
In the musical Spring Awakening, whenever a singing number takes place, the actors on stage take out microphones they've been hiding in their pockets. Like in Chicago, the idea is that whenever they're singing they're imagining it's happening on a stage in front of an audience. As such, that actually is happening, but the characters don't actually know that.
The Complete Works Of Shakespeare Abridged has the actors frequently talk to the audience, and discuss the plays they are supposed to be performing with each other. At one point, audience members are even invited on stage to participate in a scene. The ones sitting in their seats aren't left out, either.
Complete Works doesn't so much break the fourth wall as shatter it with a sledgehammer, then gleefully dance on the pieces for an hour and a half.
What happened then? Well that's the play And he wouldn't want us to give it away Not Sweeney, not Sweeney Todd...
This particular line works very well if the play is done with the conceit of inmates in a mental asylum acting out memories or scenes for their own amusement.
The second act of Into the Woods features the main characters trying to convince a giant that the narrator is Jack (who the giant is looking for) because the characters are tired of the way the narrator is telling the story. The narrator ends up being dropped to his death by the giant once she realizes he isn't Jack, and the characters now wonder who's going to tell the story since the narrator is gone.
Pretty much the whole point of Stephen Gregg's one-act S.P.A.R. (Stephen's Play About Renata) The author is summoned when the eponymous Renata holds a seance to find out about her crush Todd, and he proceeds to reveal the existence of the fourth wall. Renata literally puts her head through it and discovers the audience, and then the trope is further played out when three audience members are called to scrutinize a wall of the theater and reveal that there is another audience watching the audience. Finally, Stephen Gregg himself is called upon to scrutinize the wall, and discovers that though he thought he was omnipotent, he is in fact a character in the play-within-a-play-within-a-play. And his creator's pissed. The whole play's a bit of a Mind Screw, unsurprisingly.
As the plot of Nunsense revolves around the nuns putting on a variety show to raise money, there is literally NO fourth wall, as it's assumed that the audience came to see them perform, as opposed to a play. As such, there's a lot of interaction with the audience beyond merely speaking to them, including interaction with the orchestra pit, dancing, and a quiz for the audience to see who was paying attention to the opening.
Absolutely shattered in Billy Twinkle: Requiem for A Golden Boy, when Billy jumps off the cruise ship prop, to find that he is on a stage, and asks Sid-the hand-puppet personification of his crotchety mentor-"Who are all these people?" to which Sid replies "They're your audience, you idiot!" Yes, It Makes Sense in Context. I swear.
In Avenue Q, the characters are struggling to raise enough money. Hence their decision to go pester people who clearly have enough money to waste on things like theatre shows. They then go into the audience looking for spare change.
The Glass Menagerie opens with one of the characters explaining to the audience that this is a play based on his memories. The script comes with very detailed instructions for how to make the play appear as if it's being told through memories, although they're not always followed.
Fiddler on the Roof's Tevye speaks to the audience quite often, either to explain why he and his family are like a fiddler on a roof or to battle with his principles when his daughters break various traditions.
This is used in A Very Potter Musical, when Ron enters and tells Harry that he'd been hanging out with Hagrid backstage.
"Now that we've got that four-part harmony out of the way, why don't we look for that horcrux?"
Some theatre adaptations of Terry Pratchett's Discworld preserve the humour in the footnotes with a character called "Footnote" who sounds a horn to freeze the action, comes on stage to say the note and sets things going again.
Done beautifully by Lonnie in Rock of Ages, in which he cheers up the main character by telling him that everything he has done thus far has happened within a broadway play.
And proves it by producing the playbill for him.
Done in the final scene of Dog-Ear, when Ian and Ell discover the Scriptreader on the balcony.
and steal her script.. and promptly run off into the night.
Scriptreader: I told you there was a prop director, I told you there was a writer, I'm narrating, of course there's an Audience! Come on, do you two even watch theater?
In the most recent London revival of Oliver!, Fagin breaks the fourth wall during a few of his monologues, especially when he is play acting with his 'treasures'. For example, he was looking through an opera glass and pretending he was at a theatre, gesturing towards the Stalls in the actual theatre (where the most expensive seats are) and mentioning that was where all the rich people were, then gesturing at the top tier and saying that was full of poor people. In the second monologue he started recounting the story of the musical and ended up saying: "What the Dickens am I going on about?"
In the live-action play version of the Tyler Perry film I Can Do Bad All By Myself, Perry's character Madea is asked to leave the living room so a private conversation can be had. A couple minutes later she makes a comment and is asked why she didn't go to her room. Her response?
Madea: This is a play; ain't no room or no door up here!
Due to Peter Pan being the Trope Namer for Clap Your Hands If You Believe, the theater production of course does this. After Tinkerbell takes poison that was meant for Peter, he looks out into the audience and asks them if they believe in fairies. Then he tells them to clap their hands if they do believe in fairies in order to save Tinkerbell.
In the musical adaptation of Vanities, the cast don makeup, wigs, and costumes for each of the four scenes at on-stage vanity tables. The first scene uses Audience Participation for a cheer. In the Theatre Works Palo Alto world premiere, Mary addressed the audience during the Set Switch Song"Open Up Your Mind".
In The Prisoner of Second Avenue, Mel literally breaks one of the set walls by banging on it too hard, and the crew repair it (and the rest of the apartment) during the intermission. During scene transitions, a circle of television sets drops down and displays a Channel 6 news report to the audience.
At the climax of "The Lambeth Walk" from Me & My Girl, the company dances through the aisles.
In Assassins, during the song "How I Saved Roosevelt," Giuseppe Zangara yells at the audience for laughing at one of his lines.
In Romeo and Juliet's Unofficial, Unnecessary Sequel Prince Escalus acts as the narrator, routinely talking directly to the audience. At one point he is caught doing this by Lord Montague, resulting in the following exchange:
Montague: Excuse me, but what are you doing?
Prince: Just talking to them.
Montague: My fourth wall? Why do you call it “them?”
Prince: What do you mean your “fourth wall?”
Montague: These are my first three walls, and that one is the fourth.
Benvolio: Which is wall number one?
Montague: I don’t know. I just know this one is the fourth wall.
In the Screen-to-Stage Adaptation of Aladdin, Babkak, Omar, and Kassim frequently do this, such as commenting on prop camels and split scenes, as does the Genie during the "Friend Like Me" number.
Done wonderfully in Hair. The actors run through the audience, hand out flyers and flowers, and ask for spare change. At one point, Claude even says "Mother, the audience!"
The opera Gianni Schicchi ends with the title character turning to the audience and imploring them to clap their hands if they believe he deserves a better fate than what he got according to Dante (whose The Divine Comedy found him in the eighth circle of hell). He starts the applause himself.
In ACT Theatre's annual play of A Christmas Carol, the Ghost of Christmas Present sprinkles his torch incense on the front row of the audience. In the opening scene, the castmembers greet various audience members with "Merry Christmas".
A lot of the plays of Plautus, in fact, would begin with one of the characters giving the audience a general outline of the plot, and end with another character saying something like "Well, I would invite you to dine with me as well, but I'm sure you all have prior engagements of your own," or "So with this our story ends; give us your hands and be our friends."
The eponymous character in Pseudolus in particular seems to love this trope. All through the play we get gems such as these:
Pseudolus: ...His servant arrived here with it, bringing five hundred drachmas also, and was to take your girl away with him–but I pulled the wool over his eyes.
Calidorus: How did you do that?
Pseudolus: Well, look, this play is being acted for the benefit of the audience; they know what happened because they saw it happen. I'll tell you about it some other time.
In the recently premiered musical First Date, each of the characters addresses the audience during the opening song.
In the final Seattle run of Modern Luv, several references were made to the then-forthcoming New York run of the show. Also, the closing number dims the lights and has the audience hold up their cellphones/smartphones, as the songs lyrics say.
Fellowship! The Musical enjoyed doing this a handful of times - notably, once when Frodo tells Gandalf, "you scared me down-stage left!", and the Balrog scene, in which one character yells that they need to find an exit quickly, and another character points out the Exit sign for the theater's side exit, which they then leave out of.
In Rosencrantz and Guildenstern Are Dead, some characters (namely Rosencrantz) will look at, gesture towards, or refer to the audience. Although they do not speak to the audience directly, they do talk about them. Guildenstern at one point point shouts to the audience that there is a fire in the theater, and then wonders why the audience remains sitting calmly in their seats.
Occasionally, a production of The Mikado will have the Lord High Executioner sing (in The List song), something akin to "There's the orchestra conductor who just now has lost his place." It substitutes for a line that is (almost) invariably changed due to Unfortunate Implications in the original.
Dan Savage's Miracle!: Drag queens inviting audience members for jello shots? Check. Fake dollars handed to front row for Gloria Blaze to collect after her number? Check. Crystal Pain announcing to audience? Check. Helen blindly stumbling into the audience? Check. Beth and Winter interviewing random front row guest? Check.
In UMO Ensemble's Maldoror, whenever the characters climb on the musician's cage, he drives them off with a blast of noise.
The comedy The Miser: When Harpagon discovers his money has been stolen, he goes almost insane with grief, to the point where he begins seeing a "crowd of people assembled here", all of whom "look at [him] and laugh".
Don't give up Joseph, fight 'til you drop. We've read the book, and you wind up on top.
(And in the second chorus)
Don't give up, Joseph, just wait and see. We've been outside and you're on the marquee.'
In Cirque du Soleil's Amaluna, one of their few shows to even have a definite fourth wall, just before the show starts, Cali, the half-man half-lizard, steals a bucket of popcorn from one of the spectators, drops it while climbing the rigging, only to catch it with his tail, as well as tail-slapping others when going onstage. In a later clown act, Deeta gives birth to seven football babies with either red noses(like her) or mustaches(like their dad, Jeeves), which are handed to front-row spectators, and they have to sing Brahms' Lullaby to quiet them down. The Black Peacocks occasionally play peek-a-boo with audience members from the wings.
From Grandma's Crying by Jonas Gardell, about a family fight on Christmas, and the parents start comparing each other to characters in depressing plays.
Adolescent son: Stop it, the pair of you! You can't think like that! I mean, if this were a play by Gardell, I'd be a fag.
Mother and father: This is a play by Gardell.
Adolescent son: Shit.
In Pokémon Live!, as in the anime, Team Rocket frequently does this. Ash's Pokédex Dexter also pulls this during his song when he claims to "break out" of Ash's Pokédex when things get too difficult.
In Shrek The Musical, the still-living prisoners of Dragon tell Donkey the reason they weren't incinerated is that she keeps them around to sing backup.
In Charlie and the Chocolate Factory, Willy Wonka likes to do this on occasion. At the end of Act One, after the Golden Ticket tour group has filed into the factory, he invites the audience in as well before slamming the door shut behind him. At the top of Act Two he not only conducts his own entr'acte but briefly sits on a front row audience member's lap as he waits for the group to arrive in the Waiting Room. Finally, the last song reveals that he is leaving the onstage world for the audience's so he can continue his adventures in creativity. Note that while the Golden Ticket tour group does charge through the aisles of the theatre at one point, they nor any other character seems aware of the audience. Then again, none of them has Mr. Wonka's unique brand of sanity...
In Urinetown, Officer Lockstock and Sally directly reference the fact that they're in a play, such as at the beginning when Sally asks Is this where you tell the audience about the water shortage?" Officer Lockstock tells Sally that the audience will hear more about the water shortage in the next scene. There are other lines late in the play such as when Officer Lockstock turns to the audience and tells them that "there is no Urinetown, we just kill people."
At the end of Hamilton, after Eliza has recounted her accomplishment after Alexander died and wondered if it would ever be enough, Alexander appears and leads her out to the front of the stage, where she lets out a gasp as she looks out at all the audience members who had come to see her husband's story.
In Sergei Prokofiev's opera Love for Three Oranges the action is frequently interrupted by a Greek Chorus (or rather, four or five separate Greek Choruses) of opera fans and stagehands. This on its own doesn't quite break the fourth wall. But when the stagehands decide to intervene in the plot by kidnapping the main villain, you've got to feel like some kind of line has been crossed. Relatively rare in that the fourth wall is broken from the OUTSIDE: rather than one of the characters in the play turning to address the audience, characters from the "audience" reach in and start mucking about in the play.