Although it came out after Skyrim, the Joss Whedon and Drew Goddard film The Cabin in the Woods has been known about for years beforehand, due to a troubled development schedule (filmed in two dimensions, converted into 3D because we did the time warp back to the 80s somehow, and then MGM went bankrupt, leading to the film being shelved for a while). In Skyrim, you can find a book called The Cabin In The Woods. Appropriately, the film itself is made out of shout outs.
Sweetrolls are almost impossible to not encounter in Skyrim. Of all things, why would a Bethesda Softworks title, particularly an Elder Scrolls title have Sweetrolls as a food that heals 5 HP? Also, some guards when met with eye contact ask "Let me guess, someone stole your sweetroll?".
Sweet rolls have been a Running Gag ever since Arena, where the scene acted out in Fallout 3's CharGen dungeon is only merely postulated in CharGen (as it is in Daggerfall and Morrowind too).
In some dungeons, there are treasures resting on pressure plates that trigger a trap when you pick them up. Even better, you can even switch the treasure for something else of similar weight if you're fast enough and avoid springing the trap.
The writers of the official strategy guide clearly had a lot of fun thinking up quest sub-headers. "Hadvar's Heroes", "The Windhelm Scream", "This Means War!", "A Shaggy Dog Story", and more.
There's even a preset for male Nords that looks like Mel Gibson as William Wallace.
Delvin Mallory, a thieves guild contact in Riften, is suspiciously similar to Vinnie Jones in accent, appearance and mannerism. His voice and manner of speaking can also be seen as an homage to London Gangster films.
Lucien Lachance channels Obi-Wan Kenobi — he's a ghostly robed figure who guides the player and at one point makes reference to a great disturbance in something. In one mission for the Dark Brotherhood, he will sometimes say: "There is a disturbance in the Void."
If you talk to Imperial soldiers while wearing a Stormcloak uniform, they'll question you about it. One of your dialogue options is to state that you are, in fact, a Stormcloak — to which they call you "Rebel scum".
In Dawnstar you can meet an old soldier of the Legion named Horik Half-Hand.
In the Dawnguard DLC, there are armored dogs you can recruit. One is named Bran, and looks a bit like a direwolf.
As for the Thieves' Guild, never trust a Frey.
Lisette the bard looks like Daenerys Targaryen.
Dawnguard armor bears a striking resemblance to the armor worn by Stark soldiers in the TV series.
Back to the mammoths for a minute. They have four tusks, much like the elephants in the Lord of the Rings movies.
The design of the frost spiders, with their particularly large upper jaws, is also quite evocative of the movies' Shelob.
And Dragonsreach has a fair bit in common with Théoden's hall of Meduseld, although in fairness, they both owe a fair bit to Heorot, featured in Beowulf, but also a real place.
The whole city of Whiterun is definitely based on the Rohirric town of Edoras: Its silhouette when looking from the path to Riverwood resembles Edoras' first shot in the movie The Two Towers, its symbol shows a horse's head on the top half, and the Whiterun Guards wear a yellow uniform, when one of Rohan's colors was that same gold (if a little bit darker). The clincher is that Edoras is described in passing as having a stream which rises from in front of the door of Meduseld and flows through the whole town to exit by the gate: it's such a minor detail the fact Whiterun has the same thing must be intentional.
In Angarvunde, you find a Broken Steel Sword that bears a striking resemblance to the broken Narsil.
Nobody else noticed that Mercer Frey prying the eyes out of the giant Falmer statue in the final Thieves' Guild quest bears a surprising resemblance to the cover of the Advanced Dungeons & Dragons Player's Handbook?
Perhaps unintentional but Finn's Lute is sought for in the Bard's College.
The troll slaying guide also authored by the adventurer Finn may be a nod to the Finnish metal band, Finntroll.
In Winterhold, one of the magicians not affiliated with the College was doing a magical experiment. It ended with the creature turning inside out and then exploding, which could be a reference to either Galaxy Quest or The Fly.
While it might be a coincidence, the story of Olaf One-Eye and Dragonsreach is reminiscent of a Polish folk tale about the founding of Krakow, which states that the first king of Poland took the throne when he slew a dragon and built his castle around its lair, from which the city of Krakow was built out from.
In the quest in which the player (has the option to) obtain the horse Frost, you will also receive Frost's lineage papers. Upon reading said papers, the player will discover - among other things - that Frost's father was Sleinir. Sleipnir was Odin's horse in Norse Mythology.
Look at the Elven class of Light Armor in Skyrim. Then, look at the armor worn by the elf armies in the Lord of the Rings films.
For one of the quests in the College of Winterhold, you need to make contact with a former student. Said student was the brightest mage of his age, but after a horrible accident he took to hiding in the tunnels beneath the college.
After fighting Frostbite Spiders under Helgen, Hadvar will sometimes comment "What next, Giant Snakes?"
If you're wearing scale armor, guards will say it's "shiny".
College of Winterhold quest line. Crawling through an old underground complex. Disembodied, creepy, deep voice of Eldritch Abomination talking to you. It's first sentence you can understand? It says "You are not Savos Aren." S. Aren.Saren?
Worth noting that the spriggans look an awful lot like El Fauno.
The elves are said to be "superior at dying," which is what the Daleks said to the Cybermen during their battle in the 2006 episode "Doomsday."
In Dragonborn. there is a set of elemental powers. The Water one is called Waters of Life. "Waters of Life" is part of a recurring quote and motif in Bethesda's Fallout 3.
Likewise, the Dragonborn expansion begins with the player being ambushed by Cultists, whose orders you must read to progress the quest. Their orders reveal that they came from a place called "Raven Rock," which is also the name of the Enclave's headquarters in Fallout 3.
Hermaeus Mora himself is a walking (or floating) shout out to H.P Lovecraft and Cosmic horror in general, including his realm of forbidden knowledge, the Apocrypha and his Fish-man underlings.
The Vampire Lord transformation in Dawnguard looks like Markus from Underworld: Evolution.
Dragonborn expansion adds a book titled Confessions of a Dunmer Skooma Eater.