The Fallout series has always been filled to the brim with silly pop-culture references, from TV shows, books, movies, games, mythology, and even itself, as well as all sorts of just insane randomness. They are always fun to find, even if they break immersion a tad.
Because I'm bored, I want to share my favorites. If you're interested, you can find the full list of references here.
Unusual Call Box (Doctor Who)
I had no clue what Doctor Who was when I originally came across this. All I knew was that I had been pulled off the map on my way to The Glow and saw a big blue box and nothing else. When I walked up next to it, it disappeared, leaving behind a motion sensor.
It was a perfect "what the hell?" moment that I remembered it. I finally got my answer to what it was when I started watching Doctor Who about 5 years later (Yeah, I really shouldn't have been playing any of these games at the age I played them).
Giant Footprint (Godzilla)
Oof. That had to hurt. I guess Godzilla has moved to California. When I first saw this, I thought maybe Godzilla would be a random encounter as well, but alas, no. Although .... well, I'll see you down at the New Vegas portion for that discussion.
A classic 50's spaceship with 2 dead aliens, one holding the most powerful weapon in the game, the other a painting of Elvis. If you check the spaceship, there's a label that reads "Property of Area-51. Return if found."
The Bridgekeeper (Monty Python and the Holy Grail)
You have to answer his questions if you want to cross the bridge (especially if you want your Highwayman back, which is on the other side for some reason). He'll ask you 3 easy questions (2 if you have low intelligence). If you answer them all accurately, you can pass. If you answer his third question with another question, he dies, netting you a nice amount of XP and you can loot the Bridgekeeper's Robes off him. I always love trying to fight him, only to have exploding kamikaze Brahmin come to his aid. I'm not sure if you can actually kill him in combat though.
King Arthur and his Knights (Monty Python and the Holy Grail)
You come across King Arthur and his 4 power armored "Knights" inquiring to you about the location of the Holy Hand Grenade. If you stick around, the floating text above their heads mimic lines from the movie.
Another encounter, serving as a sequel to this one, where you encounter the knights fighting a small rat was supposed to be in the game, but was ultimately cut, although the full files for the encounter exist and can be modded back in. The rat is invulnerable to normal weapons and can only be killed with the Holy Hand Grenade, which is found in the nearby cave.
Federation Crash Site (Star Trek)
Just one of many Star Trek references in Fallout 2. You see a crashed shuttlecraft with 3 red shirts around it, who upon inspection seem to have died from dehydration. Checking the Red Shirt's body's gets you hypodermics, which are essentially the same as Super Stimpacks without the side effects. There was also originally going to be a Phazer which could be found here, but it was cut out (although all the data for it is intact and can be easily modded back in).
Guardian of Forever (Star Trek/Fallout)
This one is really fun. Out in the wasteland you come across the Guardian from the classic Star Trek episode The City on the Edge of Forever and you end up traveling back in time, ultimately resulting in you breaking Vault 13's Water Chip. Which makes the Overseer send the Vault Dweller out to get a new one, which leads to his banishment, which leads to him finding Arroyo, which eventually leads to the Chosen One's (the PC) birth, which leads to him going back and breaking the water chip, etc, etc, etc. Paradoxes for everyone!
Of course it's non cannon, but its still a fun sidequest. And it also nets you a unique energy weapon, The Solar Scorcher (although if they had that kind of tech just laying around why did I start off Fallout 1 with just a 10mm pistol and a knife?).
In Klemath, when asked about the Den, Whiskey Bob will say "You will not find a more retched hive of scum and villainy. Now where did I hear that?"
In Gecko, when talking to the Enclave officer at the Poseidon Energy Plant, one of your speech options include "Um, we're all fine. How are you?"
While the entire Fallout series is heavily, HEAVILY influenced by the Mad Max movies (Road Warrior in particular) it's even easier to see here, from the design of the Leather Armor, Dogmeat's breed (Australian Cattle Dog/Blue Heeler), the design of the raider's armor, and even a random encounter with a character called Mad Mel, who threatens you with an unloaded sawed off shotgun. Heck, they used a Road Warrior reference on the freaking case.
And seeing as I love the Road Warrior, I do love the references to it.
A utility poll near Big Town has the tag TES-04 on it. This post marks the exact center of the map.
Waste Disposal ..... IN SPACE! (Star Wars)
In Mothership Zeta, you can enter the waste disposal area during the quest "Among the Stars". Talking to Sally, you get an speech option that says "what an incredible smell you've discovered".
Fallout New Vegas
That Fridge was a Death Trap! (Indian Jones)
Outside of Goodsprings, we get to see the much more likely outcome of perhaps the most ludicrous scene in the entire series (although, I still enjoyed Kingdom more then Temple of Doom. Kill me if you must). You can loot a Gambler Hat from here.
Romanes Eunt Domus (Monty Python's Life of Brian)
In Cottonwood Cove, apparently someone's not too happy to see the Legion. Although they seem to have missed a few Latin classes. I hope they change it before Aurelius sees it. I've heard the punishment for improper grammar is quite severe.
Holy Frag Grenades
I both love and hate this one. I love it for the reasons I should love it (especially the crossed out 5 on the sign. That is a nice touch). I hate it because despite them being called Holy Hand Grenades on the sign, they are referred to as Holy Frag Grenades. Also, instead of looking as they do in the movie, they are just frag grenades with crosses painted on them. Thankfully, there's a mod for that.
EXTERMINATE! (Doctor Who)
At the Strip's North Gate, the Securitrons will shout this while in combat.
I am NOT your Mummy! (Doctor Who)
Scrawled on a pillar in a wine celler in the Villa area of the Sierra Madre Casino, this simple message makes me all the more creeped out by the villa's Ghost People.
Dog's Playing Poker
Inside the X-8 research center, we see some of the more intelligent cyber-dogs have decided to trade in the harshness of the rest of the Big MT for the fun of a life of loafing around, drinking beer and playing a few games of Poker.
Fist of the North Rawr (Fist of the North Star)
When crafting the "Fist of Rawr" weapon after killing Rawr in the Divide while having the Wild Wasteland trait, you'll craft this unique variant of it. It's exactly the same, save the name. I actually think this is the only anime/manga reference ever made in any Fallout game.
A Slave Obeys (Bioshock)
A challenge requiring you to kill Mr. House with a golf club. This has since become my preferred way to kill House on runs where I need/want to kill him (although if I feel like being particularly evil I usually just leave him alive, but disconnected from his machines).
Dead Investigator (CSI: Miami)
During the course of the quest "Beyond the Beef", you discover the body of your predecessor on the case inside one of the Ultra-Luxe rooms. Identified as Inspector Crusoe, who has red hair and wears sunglasses. I guess you could say....... I got nothing. Seriously, I sat here for like 15 minutes trying to some up with something funny or witty but I got nothing.
A petrified dog named Seymour can be found in the Cave of Abaddon in the Divide.
Cheating here a bit, Gojira is a legendary creature created by one of the animators to have some fun with. Roughly the size of a Super Mutant Behemoth, Gojira is quite literally the most powerful enemy in the game, able to kill creatures like the Legendary Deathclaw and the Legendary Boatfly easily. His breath attack is unique to him and does an insane 3,200 DPS. That combined with his obscene 8000 HP makes it easy to see why he was never going to see the light of day. His data still exists though, and he can be summoned through the use of the command console.
In my head cannon, Gojira is the offspring of the giant gecko who left the Giant Footprint back in FO1.