Beam Me Up, Scotty!: Joshua Graham's most iconic line is usually quoted as "I survived because the fire inside me burned brighter than the fire around me". In the actual game, he only says "me" once, the second time (when describing what saved him, he just says "the fire inside" with no "me" added.)
Mr. New Vegas is voiced by Wayne Newton, a.k.a. Mr. Las Vegas.
Kris Kristofferson was one of the Highwaymen, a country music Super Group composed of himself, Willie Nelson, Waylon Jennings, and Johnny Cash. Their song "Highwayman" includes a verse sung by the ghost of a dam-builder who was killed while building the Hoover Dam. Kristofferson voices Chief Hanlon in this game, and the Dam can be the death of him once again.
Big Sal is voiced by Alex Rocco, AKA Moe Greene from The Godfather, fitting his faux-Mafioso style.
Stand-up comedian Billy Knight is voiced by comedian Rob Corddry.
Dr. Mobius, who deliberately plays the role of a B-Movie villain and even admits to watching those films, is voiced by Cam Clarke, whose father Robert Clarke was best known for acting in that sort of film.
Mr. House, an eccentric billionaire played by René Auberjonois, being an Alternate Company Equivalent to Andrew Ryan from Bioshock, played by Armin Shimerman. Aside from both playing expies of Howard Hughes, these two actors played against each other in Star Trek: Deep Space Nine, and their respective characters of Odo and Quark have certain traits that filter through to their billionaire characters: Andrew Ryan embodies Quark's avarice, while House fulfills Odo's obsessive need for order.
Colbert Bump: The game helped put the real-life Goodsprings (which prior to the game was essentially a ghost town) on the map as a tourist spot. In return, the Pioneer Saloon (the real life version of the Prospector Saloon) has a framed version of the box art.
Big Iron by Marty Robbins has gained some new fans because of its inclusion in the radio.
Creator's Favorite: Chris Avellone has been open about loving Ulysses, stating he's fascinated by the idea of meeting characters the player has influenced without realizing their impact, and that Ulysses is his Author Avatar for his views on the Fallout universe.
Defictionalization: The collector's edition included chips from the major casinos in the game as well as the Platinum Chip. In a less profitable vein, many fans play Caravan in real life.
Fan Nickname: Some people who hate the Legion refer to them as "cosplayers," in reference to the fact that they're just dressing up as Roman Legionnaires.
Foiler Footage: Veronica's voice lines about Elijah after completing Dead Money were already recorded and Dummied Out in the game when it was first released. To avoid spoiling the add-on to people looking at the files, Veronica's lines were disguised with player lines about a non-existent quest to get an accelerator involving two ghouls named Abraham and Monte.
Yes, Primm is a real place, and it does have a rollercoaster (attached to the Buffalo Bill hotel — all three hotels in Primm are much larger, but no one really cares), and does have Bonnie and Clyde's death car (not his gun, though, but it does have his jacket, and the car is in a mall attached to the hotels). Hoover Dam, Goodsprings, Black Mountains, Nipton, Nellis Air Force Base, and a lot of other real-world locations are snuck in as well (mostly things only native Nevadans would recognize, like camping sites).
This is also played for a joke with "Repconn" which is a very slightly veiled joke to "PEPCON", an actual factory for rocket fuel that was formerly centered in Henderson Nevada... before it blew up on May 4th, 1988.
The Other Darrin: Christine from Dead Money has a speaking cameo in Old World Blues, where she has a different voice. Justified, however, in that it's not actually her voice she's using in Dead Money, but rather that of the long-dead Vera Keyes.
Dr. Whitely is voiced by Ron Yuan in the base game but by Jesse Burch in Lonesome Road.
Jason Spisak, who usually plays heroes, plays the villainous Vulpes Inculta.
Jason Marsden, known for playing wide-eyed, innocent young boys, voices Boone, a twenty-six year old hard-edged disillusioned Cold Sniper who lost his wife to slavers. This is especially jarring given he voiced Myron during his previous time with the franchise.
Danny Trejo voices Raul Tejada, a ghoul mechanic who's an all around kind, soft-spoken and thoughtful fellow.
Promoted Fanboy: Matthew Perry, who voices Benny and also played Chandler Bing in Friends is a big fan of Fallout 3, to the point where he got carpal tunnel syndrome from playing it to much. This lead to Bethesda offering him a role in New Vegas.
Consequently, there is also some from Oblivion, since Fallout 3 recycled some Oblivion props.
Various non-radio music from the series gets reused as well. Besides the reused Fallout 3 various songs from the first two games are used at different points i.e. the Shady Sands theme from Fallout in the Old Mormon Fort or the Redding theme from Fallout 2 playing when you encounter the Wrecked Highwayman among plenty of others.
The DLC is based around this. Originally, there was another partner character named Ulysses, who was once a part of Caesar's Legion. He was cut from the main game due to time constraints, but eventually given his time in the limelight across all four DLC mini-campaigns, culminating in Lonesome Road.
A majority of the plot itself was taken from Fallout: Van Buren, including the Caesar's Legion faction. What all didn't fit into New Vegas proper was reused for DLC, mainly Honest Hearts and the plot with Joshua Graham (who is now The Atoner instead of a Token Evil Teammate). And what didn't fit there still get scattered mentions as background lore, such as Denver being full of wild dogs or Father Elijah visiting the Ciphers tribe.
Hoover Dam was originally a Lost Colony of the NCR that had lost contact with the main government in California. The dam was a real city in addition to a power plant, while in New Vegas it's simply a power plant with a significant military presence. In both cases Caesar's Legion and the NCR are fighting viciously over it.
Van Buren was supposed to have a major war between the Brotherhood of Steel and the NCR that started some time after the defeat of the Enclave in Fallout 2 and went on into some sort of stalemate. Though several details are different, this backstory element was more or less transplanted wholesale in New Vegas.
There was originally going to be a subplot in Van Buren about a Renegade Splinter Faction of the Brotherhood of Steel called the "Circle of Steel" that used Stealth Boys for their war with the NCR. The Stealth Boys turned out to cause insanity and addiction, and their use was outlawed, but the "Circle of Steel" stole them and deserted. The Stealth Boy insanity was referenced in a few side quests in New Vegas where it seemingly only affects Nightkins, and the Circle of Steel was referenced in Dead Money and Old World Blues where they're now apparently Brotherhood hardliners and their equivalent of Internal Affairs (with Christine being a member sent to assassinate Elijah).
The Big MT, setting for Old World Blues, is a combination of the Tibbets Prison Facility from Van Buren and the EPA compound that was cut from Fallout 2. One of the appliances in The Sink, the Toaster, is based on a toaster found in the cut EPA building. The only difference between the two is that the cut toaster would simply ask you if you wanted toast (a reference to the toaster from Red Dwarf), the Toaster has a simple-minded obsession with destroying the Earth.
Saved from Development Hell: Caesar's Legion was going to be part of the stillborn Van Buren game following Fallout 2. Some NPCs from Van Buren were also recycled and given slightly different roles (Alice McLafferty and Arcade Gannon for example). The setting of Old World Blues, the Big Empty, came from the original design concepts of Van Buren's opening location, the Tibbets prison facility.
Talking to Himself: Pretty much inevitable in a game where all dialogue is voiced, and there is a huge cast of generic NPCs. It becomes especially noticeable, however, when the actor in question has a distinctive "neutral" voice. Take the four male Remnants, for example, as three of them are voiced by Peter Renaday.
Posters advertising the singer Dean Domino were made to be used as generic clutter in the base game before the design for Dead Money was locked down. When the devs noted the similarity to what they were already planning for the ghoul character, they decided to name him Dean Domino.
Trope Namer: For Auto Doc, sort of. While machines called auto-docs appeared in Fallout 2, they were pretty rare. In New Vegas and especially its DLCs they are more widespread and plot-relevant, which made the term popular enough to be used for the trope.
What Could Have Been: Obviously a lot due to the scope of the game, but also due to strict time constraints (Obsidian had only 18 months of development instead of the requested 24):
Romances were considered, but scrapped early on in development. A remnant of this can be found by looking at the available companions: of the four human companions, there's two men and two women, and one each of the men and women are gay, so hypothetically speaking, a player character of any gender or orientation would have someone to pursue.
There were early plans to extend the game beyond the final battle, but the amount of variables (ie, programming a Mojave with the victory of four possible factions and numerous minor details) made it impossible to program within the deadline. Many characters have Dummied Out voice lines for the post-endgame, and J.E. Sawyer wanted to have two new forms of money: for an NCR victory, an $500 bill showing either President Kimball or Chief Hanlon, depending on the ending, and the back commemorating the Courier; for a Legion victory, a double aureus worth 200 caps with the Courier on the back and a conquered General Oliver on the front.
Ulysses, the antagonist of Lonesome Road, was originally intended to be a companion in the main game, but was cut due to time constraints. He would have been unique among the available companions as actually being sympathetic to the Legion and especially untrusting of the NCR. Much of that personality remains in his Lonesome Road appearance, but if he'd been in the main game as originally intended, there might've been motivation to actually work with the Legion. As it stands, you can earn a pair of Luck-boosting sunglasses... but you lose the loyalty of CraigBoone and ArcadeGannon, and you'll likely end up killing at least a few factions/settlements that you actually liked. Of course, Ulysses could be persuaded to reluctantly serve the bear or another cause and will tell you about the battle of Hoover Dam.
Word of God states that there were originally more Legion territories planned east of the Colorado River, but they were cut due to time constraints. These would have included mainly civilian settlements, while all Legion settlements that remain in the game are primarily military camps.
Vulpes Inculta, Benny, and Victor were also planned to be companions before being cut. They would have supported the Legion, Independence, and House respectively, giving players some options outside of the frequent NCR-supporting companions. It does explain why Benny vanishes without a trace if you free him from Caesar.
A later interview also mentions Sunny Smiles, Yes Man, and Muggy from Old World Blues as other companions they wanted to add. The reason the latter wasn't implemented was because adding a companion through the DLCs that would work in the core game would've taken more time than allowed.
Originally, if you destroy the Securitrons under the Fort, you were originally going to be forced to fight a seriously pissed off Victor the next time you enter the Lucky 38.
Many instances of cut content (including the example directly above), have since been released in a mod series appropriately titled "New Vegas Uncut".
The New Vegas Strip and Freeside were meant to be whole zones by themselves. E3 2010 showed of the whole Strip, and it is also rendered that way in the intro cinematic. Freeside was a single massive zone, including a number of generic NPCs like beggars and pickpockets. Both instances were "sectioned off" due to the Xbox 360 and PlayStation 3 not having the necessary processing power to render all the NPCs running around the Strip and Freeside without some serious slowdown or even game crashes. The Strip just had two scrap metal gates separating it into three zones. Freeside, however, got hit harder: fences/gates made from junked buses were added, and NPCs were cut to reduce the memory problems. Appropriately, there are a pair of mods that convert the Strip and Freeside to their early open area builds.
All four of the Fiend leaders were supposed to have the Courier talk to them, rather than just Motor-Runner. Driver Nephi was the least crazed and mostly in a state of deadpan anger and he was also to be a former friend to Bert Gunnarsson and a former Mormon as well. Violet was supposed to be constantly high on Psycho and violently protective of her dogs. Finally, Cook-Cook was a fast-talkin' madman who loves his Brahmin Queenie far too much. He behaved differently towards the Courier depending on their sex; he acted more of a creep towards women than men.
According to an interview with Obsidian CEO Feargus Urquhart, the game was originally pitched as "Fallout: Sin City" and there were plans on letting you choose to play as either a Ghoul or a Super Mutant, but engine limitations regarding weapons and armor let to the idea being scrapped.
Obsidian considered making a Fallout game set in the former Los Angeles area, the Boneyard, as Fallout: New Vegas 2, or Fallout: Los Angeles.
Very early on, the game was pitched as an Interquel set in between Fallout 2 and Fallout 3. This was shot down by Bethesda, as they apparently have a policy about only making sequels (until Fallout 76).
Like with Fallout 3, there were some loose plans to include the Floater enemies from Fallout 1 and 2, but due to time constraints this was dropped early on. They're still Dummied Out in the game, using the Centaur's model. Word of God is that they were cut since the animation team didn't have time to do a proper skeleton and animation for such an odd creature.
It was initially possible to negotiate a peaceful solution between Mr. House and the Brotherhood, as evident by an optional objective left innote evidence suggest that, much like with the NCR and Yes Man routes, doing so would've involved getting the Brotherhood to support the NCR; however, said feature was eventually dropped, as director Josh Sawyer felt it wasn't true to Mr House's character. Whether or not this would've lead to the Brotherhood fighting alongside a House-aligned player in the final battle or if they would've just ignored the finale is unknown. Much like with other cut content, mods restore this functionnote for those who put Hardin in power and for those who keep McNamara in charge.
There is also a note in which Mr. House agrees to let the NCR annex the New Vegas Strip in exchange for NCR citizenship and immunity from prosecution.
Two alternate endings to the Dead Money DLC were cut: one had the Courier die in the Sierra Madre Vault after FatherElijah turned it into a Gas Chamber. The other involved Christine Royce killing Elijah and trapping the Courier in the Vault.
Old World Blues was supposed to have a particularly horrifying Downer Ending where you could side with the Think Tank and unleash their experiments on the Mojave.
The game files contain an NPC labeled "Vault 11 survivor", indicating at some point it was planned for the player to be able to meet him in person.
According to Chris Avellone, the original NCR-Brotherhood war would have been far more tragic than it is in the finished version. Originally, the NCR mistakenly believed that the Brotherhood and the Enclave were one and the same because due to their shared use of advanced pre-war technology. When the actual Enclave nuked San Francisco in revenge for the Oil Rig, the NCR would retaliate against the Brotherhood believing that they were responsible, thus setting off the conflict.
Welcome to Corneria: Dr. 8 in Old World Blues does have dialog, as shown in the game's text files. However, he has a limited amount of responses to the Courier's lines, often repeating them in the same conversation.
The Developers were undecided whether Benny would betray you again or become your Companion if you spare his life in Caesar's tent. In the end neither option became canon. His becoming a Companion would have taken too much time and resources, so it was scrapped. The devs put in a scene where he betrays you, but took it out of the finished game. So, if he lives, canonically he just keeps his promise to "get out of your hair forever."
"Caesar can quote Cato to his purpose" is a paraphrase of a line from The Merchant of Venice: "The Devil can cite Scripture to his purpose." (Though Shakespeare is pithily reflecting much older wisdom.)
"Am I playing Vergil to your Dante?": The Divine Comedy, where Vergil serves as Dante's guide through Hell.
"Victrix causa diis placuit sed victa Catoni." is from Pharsalia by Lucan. Translated it is simply: "the winning cause pleased the gods, but the losing cause pleased Cato." Considering its context, it fits very well.