"In the mid 1980s I was asked to compile a comic book detailing the murky history of the CIA. What I learned during the frankly horrifying research was that, yes: there is a conspiracy. In fact, there are a great number of conspiracies, all tripping each other up."
Everything you've heard is true: The Illuminati rule the world, the moon landings were faked, JFK was assassinated by a bunch of gray aliens, and you surely don't think the Cuban Missile Crisis was about Cuban Missiles, do you?
Yes, that's right: In this setting, every conspiracy theory you've ever heard of is true. And some you haven't. A closely related subtrope to Fantasy Kitchen Sink, but conspiracy-minded, rather than fantastic; like its parent, there is a certain tendency towards self-contradiction, but given the source of the trope (paranoid conspiracy theories), not that surprising.
Following things are a must-have for any Conspiracy Kitchen Sink worth its salt (for required tropes, see The Index Is Watching You):
A lot of Grant Morrison's other work, features loads and loads of conspiracies. The Invisibles deserves special mention though, since it takes place in a world where pretty much every single piece of conspiracy literature scrawled out in the last 60 years was all true. Simultaneously.
The main protagonist of Hunter-killer (written by Mark Waid) has been home schooled, and what he's been taught (as far as recent history is concerned) is all conspiracy theories. And not surprisingly, all he's been taught is true, except the part about the week having six days. One major turning point, as it turns out, was indeed the Cuban missile crisis.
In The Question's spotlight issue of the Justice League Unlimited tie-in comic, he spends a week solving every major conspiracy in western civilization's history. Stuff like "Jack the Ripper was cloned from the Chupacabras that landed in Area 51". It turns out a lot of it was faked, but that's the kind of stuff he makes a living investigating.
The Matrix Reloaded. The Oracle tells Neo that the Matrix is full of programs controlling its individual elements.
Oracle: The ones doing their job, doing what they were meant to do, are invisible. You'd never even know they were here. But the other ones, well, we hear about them all the time.
Neo: I've never heard of them.
Oracle: Oh, of course you have. Every time you've heard someone say they saw a ghost, or an angel. Every story you've ever heard about vampires, werewolves, or aliens, is the system assimilating some program that's doing something they're not supposed to be doing.
The Men In Black movies seems to represent a peculiar version of this — every conspiracy theory you've ever heard is on to something big, but the truth behind all of them is the same, in this case aliens.
One example is a small ball that seems to be similar to rubber, except it GAINS energy with each bounce making it incredibly destructive. Apparently it caused a massive New York blackout. The alien diplomat who did it? He thought it was funny as hell.
James Ellroy's American Tabloid answers the question "Who killed JFK?", with a pretty resounding "Everybody". (If you want more specificity: the assassination was bankrolled half by reactionary billionaire Howard Hughes and half by various Mafia bosses, the shooters were CIA contractors borrowed from one of the Company's many anti-Castro black ops, and J. Edgar Hoover personally directed the cover-up in the hours after the shooting.)
The Illuminatus! trilogy of novels by Robert Shea and Robert Anton Wilson. FNORD
Why did someone put in a spoiler block with nothing in it?
In Conspiracies, Repairman Jack attends a Conspiracy Theoristconvention. Subverted in that there really is a conspiracy happening behind the scenes ... but it's against Jack himself, not anything the convention's attendees dreamed up.
I, Claudius is a hodgepodge of pretty much every half baked conspiracy theory about the time of the Julio-Claudian Emperors, both then and since.
Anything written by Dan Brown. The Robert Langdon books have had a habit of subverting this trope, however. While conspiracy theories are often thrown around by the characters, there usually ends up being a logical, or at least somewhat realistic explanation for everything. In fact, Conspiracy Theorists have ended up being the villain more often than not because they believe that nothing is true and everything in permitted.
The Onion published an article about the JFK assassination that made use of this trope. "Kennedy Slain By CIA, Mafia, Castro, LBJ, Teamsters, Freemasons: President Shot 129 Times From 43 Different Angles".
This is the entire purpose of Mr Blank and its sequel Get Blank, a detective story in which the hero works for literally every conspiracy there is, so when someone tries to murder him, there's no shortage of suspects. One of his most reliable tactics is playing off one conspiracy against another such as pitting the Little Green Men against the Assassins and the Russian Mob in order to rescue his girlfriend.
"Everything You Know Is Wrong" by Chumbawamba, where the narrator claims responsibility of e.g. "taking scissors on the black vote down in Florida", "I was there when they landed on the moon, in a studio in Kentucky in June", "at the canteen down in Columbine, with the bags they never found", "and I hid those missing WMD's"...
The Crucial Conspiracy, The Dingees' third album, had references to chemtrails, government mind-control experiments, and Majestic Twelve; and even has lyrics that could be interpreted to mean that Satan himself is involved in UFO activity.
Conspiracy X is an RPG (by Eden Studios) based around the concept of some or all of the conspiracy theorists being onto something.
Delta Green is a modern-time setting for the Call of Cthulhu RPG. Not only is every possible conspiracy staged by either Nyarlatotep, Mi-Go, or some other Eldritch Abomination, but the playable organization, Delta Green, is an illegal conspiracy. Why? Because official paranormal investigators are controlled by aliens, of course.
What's even funnier is that, in the official setting, Delta Green doesn't believe in aliens, only monsters, magic, and ghosts. Of course, anyone who's up on the source material know that all the monsters, aliens, and magic reside at the same address. (It's also worth mentioning that the aliens who are controlling the official MIB aren't actually aliens, but artificial constructs created by the real aliens who wanted a weird but still recognizably human appearance.)
Steve Jackson Games has at least three products set here:
The various Illuminati card games (inspired by the above Illuminatus! trilogy).
GURPS Illuminati (inspired by the success of the card games).
Depending on how you look at it, In Nomine (and its offshoot, GURPS In Nomine) also qualifies.
In Nomine Anime, a small and obscure supplement, definitely has one foot in this territory.
Also GURPS IOU. The "I" does stand for "Illuminati" after all. (The "U" stands for "University", and the "O" stands forYOU'RE NOT CLEARED FOR THAT INFORMATION! ...seriously speaking, it's never explained.)
Paranoia, an RPG originally by West End Games, though it's set in a futuristic dystopia and not the present day, definitely falls under this trope.
This is largely because early books weren't necessarily written with crossovers in mind, and gave you a world populated by one supernatural threat, later books in oWoD got better about enabling crossovers and finding niches for the various creatures.
The Technocracy, in particular, seemed to have a handle on vampires and werewolves better than anyone else... then it turned out the Technocracy contained several competing conspiracies.
The New World of Darkness is getting there, too, except none of the conspiracies control everything, just a specialized area. The Seers of the Throne make sure that magic stays out of the Fallen World so they get it all to themselves. They have their own phony Men in Black, Division Six... and we say "phony" because the real Men in Black, Task Force: VALKYRIE, operate out of the US Treasury. Then you have the medical corporation that performs experiments on supernatural creatures to find out how useful their parts are, the Catholic Church's crack monster-hunting squad, and the FBI bureau staffed with psychics who hunt down supernatural serial killers and stick them in a Midwestern Guantanamo. And so on. (It's worth noting that all of the listed examples, excluding the Seers of the Throne but including Division Six, come from Hunter: The Vigil.)
And in the Fanmade Gameline Genius The Transgression, Lemuria used to be in charge of this, but now only thinks they're in charge of it. (Bizarrely, the Lemurians and the Seers of the Throne are unable to detect each other, and no-one knows why.)
One character claims the maintenance men at his workplace are plotting against him when he gets a lemon-lime soda from a vending machine when he was almost certain he pressed the orange button. His partner is skeptical, to say the least.
Anna: Are you sure you pressed the right button?
Gunther: I do not make mistakes of that kind!
Anna: Your hand might have slipped.
Gunther: No, I wanted orange. It gave me lemon-lime.
Anna: The machine would not make a mistake.
Gunther: It's the maintenance man. He knows I like orange!
Anna: So you think the staff has some kind of plot?
Gunther: Yes! They do it on purpose!
Entertainingly, this is confirmed in the sequel by a NPC.
Bum: Someone here must have really liked lemon-lime soda.
Let's see... Area 51, Majestic 12, the Illuminati, lab-designed plague to cull the lower classes, the Greys, black helicopters, Men in Black (much closer to the original concept than the ones in the above movie), Chupacabras (called "greasels" in the game), FEMA as a black organization, New World Order, corporate takeover of government...
Metal Gear Solid 2 parodied itself at one point by having one of the on-disc supplementary story recaps being a book written by the most hilariously deranged conspiracy theorist you could possibly imagine. (To give you an idea; we don't get to read it, but the title of his previous book was Rays From The Loch Ness Monster — The True Power Source Of UFOs.) To his credit, he was extremely good at identifying conspiracies — unfortunately, he never blamed the events on the right conspiracies, attributing The Omniscient Council of Vagueness-caused disaster of the previous game to the island it was on being "an Ellis Island for the Greys". The whole farce ends with him being rescued by an invisible man whom he proudly, loudly declares is a noble Sufficiently Advanced Alien who had taken pity on him, when it's clear to the reader that it's Solid Snake in active camo.
Assassin's Creed rapidly became an amalgamation of all sorts of conspiracy theories, incorporating everything from the Tunguska Event to JFK's assassination to the entirety of World War II and tracing them all back to the Templars, the Assassins or both trying to cover up or seize something or other. It's not exactly necessary to understand how it all fits together to make any sense of the plot, fortunately, because any attempt to do so is doomed to failure, particularly when time travelling god aliens get involved. Generally it's best to simply accept that the Assassins and Templars have been at each other's throats for a really long time and move on. Gets especially crazy and paranoia-inducing in Assassin's Creed: Brotherhood. Alan Turing? Murdered to prevent him from inventing too powerful computers. Cable TV? A method for transmitting brainwave altering signals and monitoring citizens. Cell tower surveillance? Tracking all communication.
Though it's not essential to play the game, the hidden messages in The Conduit meshes together just about every conspiracy theory under the sun. Especially the sequel.
The Church of the Subgenius (a tongue-in-cheek parody of both New Age mysticism and Fundamentalist Christianity, fused together) includes a deliberately mixmastered hodgepodge of conspiracy theories in its whacked-out "cosmology". Take two shots Discordianism, three ounces of unadulterated conspiracy theory, shake together with a splash of Bay Rum, a pinch of Dianetics, and a heaping helping of LSD, and you might be able to approximate it. Drink straight from a Klein bottle for maximum effect.
David Icke will tell you that the Anunnaki, ancient Babylonian gods, were in fact Reptilian aliens who are still among us, among them the Windsors, Bushes, and Habsburgs, and are behind every conspiracy ever alleged, including Kennedy, 9/11, the Pyramids, anything involving Illuminati, etc. (especially the antisemitic ones), authors of the past using then-acceptable antisemitism to pass coded references to Reptilians to others "in the know."
His theories are so well-known and crazy that Lost Tapes did an episode concerning Reptilians that's basically a loving homage to his kookiest and craziest theories. It also ends with a slight twist. The Reptilians aren't here to rule and manipulate us, they're here to harvest us.
Most "unified conspiracy theories" are deliberate examples of this, being attempts to shoehorn every conspiracy theory that the writer believes into a coherent narrative.
Above Top Secret is a massive example of this trope, being a large website and forum devoted entirely to conspiracy theories.