Several of the quests are named after song titles.
You can find a farm with two damaged farmhouses, a pickup and burnt down house with a dead body. Upon finding all four pages of the body's diary (one on the truck, one in each farmhouse, one in the house) you will learn that his parents were turned into Feral Ghouls, he killed them, and then thought that the animals were plotting to kill him and take over the farm.
There's a very subtle one that they really had to do the research to dig up - there's a minor, otherwise unimportant member of the gang known as The Kings carrying a unique barber's razor called Figaro. Examining the map reveals that the location he is found in corresponds almost exactly to the location of the real life Figaro's Barber Shop in Las Vegas.
House's obituary contains a small shout out to Lolita.
You can be forgiven for expecting the first words of his giant, green-headed avatar to be "I AM OZ!"
After your first meeting with him, Cass actually advises you to look behind the curtain.
Another Oz reference is in Old World Blues, where the Courier has his brain, heart and spine replaced with cybernetics and is given the respective perks "Heartless", "Brainless", and "Spineless", referencing the Scarecrow, Tin Man, and Lion's predicaments.
When you finally confront Mobius to get your original body parts back, he says it reminds him of a story about "a band of murderous thugs" went on a journey to get "brains, a heart and courage...spine". For bonus points, the interior Mobius's lair is emerald-tinted.
You can find a BFS made of a car bumper that's about seven feet long. What's it called? The Bumper Sword.
A dead prospector located in a heavily irradiated area called the Devil's Throat bears a strong resemblance to Duke Nukem.
Those versed in US finance will recognize NCR bear and the Legion's bull as symbols of the stock market, the bear and the bull traditionally representing a falling and rising market respectively. The NCR falling while pushing east, and the Legion rising with their conquests.
A unique weapon in the game is "This Machine," named after Woody Guthrie's guitar "This Machine Kills Fascists." In response to that name, the phrase "Well This Machine Kills Commies" is written on the side of the gun.
Speaking about weapons, That Gun got its name because... well, it's ThatGun from Fallout 2.
During the quest "How Little We Know" you meet a man who's indebted to the Omertas because they helped him cover up his accidentally killing a prostitute during a drug-induced blackout (which was actually set up by them in the first place). Now why does that sound so familiar?
The Bright Brotherhood ghoul cult is preparing to embark on a "Great Journey" to the "Far Beyond", and refer to the Nightkin attacking them as "Demons".
A subtle and possibly unintentional one comes courtesy of the Terrifying Presence perk, giving a unique dialogue choice when dealing with some Brotherhood of Steel members, threatening to destroy the Brotherhood and "cast down their Codex" (their doctrine). After the BoS members run off, Veronica worriedly asks if you were joking about the Codex. It makes sense In-Universe as Veronica doesn't want you to destroy the Brotherhood, but it may also be a subtle nod to her voice actor, Felicia Day, whose character in The Guild goes by the handle of "Codex".
Mr. New Vegas's news blurb about the simmering tensions in Freeside consists almost entirely of him quoting the King's Incredibly Lame Puns referencing various Elvis songs.
When crouching with Cass in the party, she will occasionally mutter "shhh, we're hunting shitheads" like a foul mouthed Elmer Fudd
Let's just say that Goons will be playing in utter glee with an appearance from Johnny Five Aces and company.
Just outside Goodsprings you can find a refrigerator with a skeleton in it. It's wearing a brown fedora. May double as a Take That, since many people couldn't get over the fourth film's nuclear explosion.
On the wall in Cottonwood Cove (a Caesar's Legion outpost) is graffiti reading "Romanes eunt domus."
In Nipton you find a pair of clothed, charred corpses outside of a house named Owen and Beru.
One of the more subtle Wild Wasteland occurrences is when you're exploring a disappearance in the casino of the White Glove Society: you discover the body of a fellow detective, a sunglasses-wearing man by the name of Caruso.
Even better, you can also hear "Game over, man, game over!"
It was cut from the final game, but the game files show that there was supposed to be a creature that could only be encountered in Wild Wasteland: A unique Fire Gecko that had its own unique breath weapon, was three times larger than normal fire geckos, and could best the Legendary Deathclaw in combat, making it the most powerful creature in the game. When spawned with the console it's just "Gecko," but its name in the editor is Gojira.
A mod restores this, with an added script that spawns it after killing the four legendary creatures in the base game.
Besides that, the casino contains the Tampico Theatre (named after the town Bogart and Co. set out from in the film) and the Cantina Madrid (where Bogart and his partner... negotiated aggressively with their fraudulent boss). The "Police Pistol" added in the DLC is also the same model of revolver used by some characters in the film.
The entirety of the Sierra Madre itself - an abandoned 'town' surrounded by an ominous fog, populated almost exclusively by unkillable Humanoid Abominations, and people who're trapped there without realizing they're dead, where radio static warns of imminent danger - will seem very familiar to certain people.
Don't forget the very, very unsettling ambient music.
Sinclair's revenge plan for Dean Domino is a reference to Edgar Allan Poe's short story, "The Cask of Amontillado." In it, a man entombs a fellow nobleman alive. Sinclair even refers to Dean as Fortunato, the nobleman from the story, in the note he leaves in the vault, which is programmed to slam shut and lock after it is read.
Elijah's speech to the Courier through a circular green screen in the vault is also obviously based on the eponymous wizard of Oz.
With Wild Wasteland, one of the tribals is named "Two-Bears-High-Fiving." This is in reference to a rather peculiar New Vegas mod. The mod's author was apparently very bothered by the fact that there's no dialogue that states one of the Rorschach ink blots Doc Mitchell examines you with looks like two bears high-fiving. Said mod is solely dedicated to adding that single dialogue line in.
Also with Wild Wasteland, talking to White Bird the shaman about the Rite of Passage causes him to say "Take drugs, kill a bear," a reference to the Advice DogImage Macro.
Quite a bit of Old World Blues makes subtle reference to The Venture Bros., with Dr. 0 being voiced by James Urbaniak (the voice of Rusty Venture) and having his personality and many of his lines lifted directly from the show.
You can even find miniature versions of the Walking Eye with the Wild Wasteland perk.
Dr. Klein, although not voiced by the same actor, sounds suspiciously like Jonas Venture from the same show.
Dr Borous said he created Nightstalkers and Cazadores back before the war, he can't remember exactly when, but he rememberedit was Tuesday.
In the doghouse behind Dr. Borous's house, you can find a miniature Deathclaw named Stripe.
In one of the research labs, you can observe a room with Cyberdogs sitting around a table... poker.
The food source of the Think Tanks is Salient Green, although it is not made from people.
Speaking of Soylent Green, the sacrifice chamber in Vault 11 resembles the euthanasia booth from the film.
The revealed origin of Cazadores, they were genetically modified to be giant deadly creatures, but were never intended to leave the lab, nor did the scientists acknowledge they were still able to breed. Sound familiar?
The Big Empty may be a reference to a 2003 film of the same name, which takes place in Baker, CA, halfway between LA and Vegas.
A minor one, but if one searches they will find that there are three locations within the US referred to as Big Mountain. One of them is Black Mesa.
The Think Tank regularly mispronounce impossible as "unpossible," which is what Ralph Wiggum said in The Simpsons when told he was failing English.
A cave can be found (and you're required to visit it for an optional side-quest) that is home to a number of toaster-worshipping Lobotomites, including the first Lobotomite test subject. The name of the cave? The Cuckoo's Nest.
"Like one that on a lonesome road / Doth walk in fear and dread, / And having once turned round walks on, / And turns no more his head; / Because he knows a frightful fiend / Doth close behind him tread.”
Nuking both NCR and the Legion at the end of Lonesome Road with Wild Wasteland on will turn a part of Ulysses' closing narration into an almost word-for-word reference to the infamous ending of Planet of the Apes, as well as showing the Mojave Outpost Monument half-buried in sand like the Statue of Liberty.
The bad guy from Ralphie the Robot, General Winter, in addition to being an Internal Homage to Fallout 3's Colonel Autumn, is also a Russian figure of speech referring to the harsh Russian winter's ability to stymie invading armies, most notably those of Napoleon and Hitler. General Winter's won Russia a lot of campaigns.
Gun Runner's Arsenal
Fan FilmFallout: Nuka Break gets one in this DLC, before it's even released! A new unique rebar club is added in the game. Its name? The Nuka Breaker.
Now that it's out, it's special move is in fact called the "Nuka Break."
One of the One-Star Challenges added is A Slave Obeys. For those who never played BioShock, you kill Mr. House with a golf club.
Another assassination-related Challenge is "Even A God-King Can Bleed," which you get for nailing Caesar in the head with a throwing spear.
The challenge for killing Caesar with a knife is called "Historical Propriety," as it's a repeat of how the original Caesar went down. Bring Arcade Gannon for added bonus, as he has the historical knowledge to appreciate your effort.
Everything from the White Line Nightmare challenge, the name the weapons and the enemies, is a reference to Mad Max 2