The Kingsguard, and later its derivatives, the Queensguard and the Rainbow Guard, of A Song of Ice and Fire. They're supposed to be made up of the seven greatest warriors in service to the monarch at that time, and for most of their history, they are. Deconstructed with the Kingsguard; they used to be appropriately badass, but after Robert's Rebellion leads to all but 2 of them dying and getting replaced with fighters of lesser quality, things start to go to hell quickly. At the end of the first book command of the Kingsguard is transferred to Jaime"Kingslayer"Lannister, and things go further downhill from there. As the books progress, more members of the Kingsguard die in the war, and their replacements, instead of being selected for their skill with a sword or devotion to duty, are chosen for political reasons. Cersei eventually ensures that with the exception of Jaime (who is crippled and away at war), Balon Swann (who has been sent south to Dorne) and Loras Tyrell (who was badly injured while trying to take a castle) all of the appointees are terrible fighters—so when she frames Queen Margaery for treason, Margaery has no choice but to select an incompetent fighter for a champion in her trial. It backfires spectacularly when Cersei herself is charged with treason. Also somewhat deconstructed with the Queensguard, in service to Dany, as it has never had more than one member at a time.
Most lords have a household guard led by a captain who are usually the best fighters in their realms.
Robb Stark has a guard made of sons and daughters of Northern and Riverland lords.
Previews from The Winds of Winter show that the Vale is organizing an eight-member group called the Brotherhood of Winged Knights to serve as young Robert Arryn's bodyguard until he comes of age.
The Lord of the Rings has a number of guard units, most notably the Citadel Guard of Minas Tirith which Pippin joins.
The Deathwatch Guards from Seanchan in The Wheel of Time. Most non-Borderlander countries have elite formations that serve this purpose (the Companions of Illian, the Tairen Defenders of the Stone, Mayene's Winged Guards, and the like). Then there's the Dragon Reborn's personal Maidens of the Spear, who have a "complex" relationship with Rand.
Elayne has the Queen's Guard, a unit of women whose uniform is designed to make people underestimate them.
The Fanatical Praetorians in Daniel Pinkwater's Young Adult Novel, a bunch of short guys in sailor hats organized by Kevin Shapiro to protect him, issue his orders, and intimidate even the teachers at Himmler High School.
Sword of Truth: The Lord Rahl has two sets: Musclebound male bodyguards, and two thousand elite soldiers known as the First File. After Richard frees the Mord-Sith, they become a third set.
Jagang has his elite core of soldiers that guard him and spearhead assaults with the rabble as extra weight. They are bigger, tougher, stupider, and better-armed than the normal troops.
Grayson steadholders (effectively higher-level nobility in command of the equivalent of states) has the Steadholder's Own tasked to protect them, though each Steadholder is limited to 50 armsmen to prevent anyone building up a private army. This actually becomes a bit of a problem, when Honor returns to her duties as a RMN officer. Since Grayson law demands that a steadholder never travels without his (or her) guards, this comes into conflict with the RMN regulation forbidding non-RMN personnel walking around armed aboard RMN warships.
At one point, Honor inadvertently creates a constitutional crisis when she forms The Elysian Space Navy, due to the above limitation on personal armsmen. This is averted by having her hand control of it over to Protector Benjamin, ruler of Grayson, who renames them The Protector's Own Squadron, effectively giving him a Praetorian Fleet.
Then there is the Queen's Own tasked to protect the Manticoran Royal Family
The Totenkopf Hussars which serve as the household guard of the Andermani Emperor and his family.
The People's Republic of Haven uses foreign Space Swiss mercenaries — they certainly wouldn't trust their own people. Their paranoia is justified, and the next government who rises to power after killing off the previous government uses State Sec troops for their personal guard.
The Emperor of Videssos (A Fantasy Counterpart Culture of the Byzantine Empire) from Harry Turtledove's books has a guard of pagan Halogai warriors. This may seem rather unlikely in a culture so obsessed with the doctrinal purity of their religion, but apparently the logic is that the Halogai can't get involved in such denominational squabbles and the palace intrigue that goes with them. And it's Truth in Television - the real Byzantine Emperors had a Varangian (Viking) Guard.
The Prince Roger Series is all about one of these units- with its work seriously cut out for it. Within the first chapter, a plot by ambitious politicians of the Empire leads to the spoilt, nancy third-born prince and his Bronze Battalion being stranded with him on a serious Death World. It got worse, much worse ( and the prince got better).
The Palace Guard in early Discworld books, most notably Guards! Guards!. In later books, while Vetinari does keep the guards and gives them orders to accept all bribes, he relies mostly on Vetinari Job Security (and, if entirely necessary, his own assassin skills) to keep himself alive. While still active in later books, Vetinari reduced their role with the introduction of Dark Clerks, unobtrusive, quiet, and efficient staff that just happens to be mostly drawn from the most promising graduates of the Assassins' Guild.
A number of the Primarchs in the Horus Heresy series have Praetorian guards of one stripe or another - Fulgrim's Phoenix Guard, Ferrus Manus's Morlocks, Mortarion's Deathshroud, Sanguinius's Sanguinary Guard (not yet appearing on the page, but the recent re-release of the Blood Angels codex includes them). There are probably others, whose primarchs have not had their day in the limelight yet. Some definitely don't these, though, in particular thus far, Horus, Russnote well, strictly speaking, he had the Wolf Guard, but they seemed to be used more as his public foil, rather than as a bodyguard and Magnus. Angron splits the difference by having a set, the Devourers, but not caring they exist. The Emperor's are the most badass of all though - the Adeptus Custodes, who are to super soldiers what super soldiers are to regular soldiers. And that ignores all the army commanders who have their own, including the infamous Lucifer Blacks in Legion whose leader is possibly the single most Badass Normal in the entire setting, after fencing a primarch to a standstill with an unpowered sabre, and wounding him.
In Falkenberg's Legion, Vice President Bradford attempts this. He has Falkenberg organize a brigade composed of trusted party members and officers loyal to Bradford. Unfortunately for him, Falkenberg uses the would-be Praetorian Guard to take the brunt of the fighting.
The government of Hadley also has a formal Presidential Guard, but their loyalties are questionable.
In Sergey Lukyanenko's Seekers of the Sky duology, the State (the Europe-spanning empire) had Praetorian Legions as elite troops. Several such legions are mentioned with the Grey Vests being the most badass (they all had guns, a rarity in this world). Their counterparts in the Russian Khanate are the Semetskiy Guards. Nothing is known of the counterparts in the third power, China.
The Imperial Royal Guards wipe out small armies by themselves. Before the Empire, they were the Red Guard and were the security detail of the Supreme Chancellor.
The Senate Guards and Senate Commandos during the Clone Wars, who are in charge of the protection of the galactic senators and representatives and can also assist regular forces on some missions. They are also humans for the most part, and not clones, unlike the regular army. They are considered an elite group.
In The Courtship of Princess Leia the Hapan Royal Guard are introduced, tasked with safeguarding the Hapans' royal family.
Even better fitting the trope, Star Wars: Legacy's Imperial Knights start up in this series, courtesy of Tahiri Veila.
The Jedi Temple Guards are this to the Jedi Order.
In the Hand of Thrawn duology, Grodin Tierce was a Guardsman who had survived fifteen years after Endor, choosing to appear as a normal soldier because to do otherwise would be to seek special privileges. He served as the tactical, planning part of his Big Bad Triumvirate, though bit by bit he became more and more important in it. Really he was a clone of the now-dead Guardsman Tierce, with some of Thrawn's mind added in.
The X-Wing Series had a more minor appearance. In The Bacta War, Ysanne Isard had a few Guardsmen around. The viewpoint character, unaware that the armor includes AC, pitied them. This was in a hot climate, and they had heavy scarlet robes.
The Purge Troopers are this to the Inquisitorius made up of both clones and non-clones alike.
The Slayers, named in honor of the Yuuzhan Vong war god, from the last book of the New Jedi Order.
As it is set in the Byzantine era, they show up frequently in the Belisarius Series:
Kungas and his Kushans serve as this for Shakuntala. Interestingly she knew them first as her prison guards but they were so effective and conscientious at this that she was perfectly happy to have them as bodyguards. They in turn were happy to serve a monarch they could respect.
The Ye-Tai are described as performing this role for the Malwa. As they are outside the caste system, their high place in the social hierarchy is entirely due to their role as the Malwa's elite soldiers.
Discussed, with regard to Link's assassins. As an elite, they are highly trained but frequently have little actual experience. "As Praetorian Guards have done throughout history, they had slipped from being killers to murderers."
Subverted with the Steel Inquisitors in Mistborn. Yeah, they're by far the most badass of the Lord Ruler's minions and a couple of them accompany him at all times, but that's mostly because he doesn't like to do his own dirty work. He's actually far more powerful than any Inquisitor, illustrated in the climax of the first book when two characters take care of almost all the Inquisitors in the capital city and think they've won the revolution, only to be curbstomped by the Lord Ruler himself effortlessly.
Also, the Orff, a race of aliens who act as security agents to the Council of Thirteen.
In The Dresden Files series, most notably seen in Summer Knight, the Fairy Queen of Summer and Fairy Queen of Winter both have respective Knights who would hold a piece of their power in exchange for loyalty and protecting them.
In the Vorkosigan Saga, each Count of Barrayar is limited to twenty armsmen to prevent them from having large private armies that could threaten civil war. Naturally every armsman is a badass. Armsmen are assigned not merely to guard the count and his family but to carry out local police duties.
The Aristoks of Fiona Patton's Tales of the Branion Realm have three distinct forces - the commoner Palace Guard, the noble Shield Knights, and the religious Flame Champions.
Reynard creates one to defend himself in between the events of The Baron of Maleperduys and Defender of the Crown.
In the Tortall Universe, there are three basic military bodies in Tortall: the knights, the army, and the Queen's Riders. There is also the King's Own, composed of a variety of knights, soldiers, and fighters all dedicated to the King (specifically, Jonathan), and who act as his bodyguard. For the vast majority of the series, Raoul acts as their leader, while Sir Alanna acts as the King's Champion.
In The Lost Regiment, the Vushka Hush are the elite warriors of the MerkiHorde. They comprise several full umens (a full umen is 10,000) of finest warriors the Merki have to offer, being both excellent mounted swordsmen and horse archers. When going into battle, they chant "Vushka! Vushka!", sending fear into their enemies, especially since the Merki are 9-foot-tall and love the taste of human flesh. And yet, the titular regiment (the 35th Maine Volunteer Infantry) along with their Rus' and Roum allies manage to gut the Vushka, using American Civil War-era weapons and training to counter the numerical advantage of the enemy.
The Age of Fire series has the griffaran, the dragon/griffin-like creatures that serve as an outer layer of defense for the Lavadome, as well as personal bodyguards of the Tyr.
The Regiment in Hammer's Slammers has the White Mice, the personal guard and military police of Colonel Alois Hammer. In later novels, the old Regiment, after conquering Nieuw Friesland, becomes this.
The Tyrant's Guard in The Dinosaur Lords, who serve as bodyguards and policing force to the Emperor of Nuevaropa. The "Tyrant" in the name refers to T. Rexes.
In Words of Radiance, Bridge Four becomes the Praetorian Guard of the Kholin family after most of their previous bodyguards died in the Battle of the Tower in The Way of Kings (2010).
The King's Guard at the start of the series, though that's about as far as they are described.
During Royal Assassin, Queen-in-Waiting Kettricken acquires her own Queen's Guard, who are inspired by her own courage and prowess in battle and decide she needs her own guard.
The Crimson Shadow: Cyclopian soldiers named this not only guard King Greensparrow but also serve as elite troops.
In The Witchlands, the Marstoki Adders are the elite bodyguards to the Empress of Marstok. They're notable in-universe for every member being a Poisonwitch.
The Queen's Thief series, by Megan Whalen Turner, has two examples, one heroic and one villainous. Attolia has the Palace Guard, who serve primarily as the personal bodyguards of the king and queen, although their complete devotion to the queen also makes them a core part of the regular army during times of war. By the end of the third book, the Genre Savvy king has made plans to halve the Guard specifically to avoid the possibility of a Kingmaker Scenario. The fifth book introduces the Namreen, loosely based on the Immortals of the Achaemenid Empire, who are the personal guards of the Persian-esque emperor and pose the greatest threat to the protagonists for most of the book.
ISF Marines start guarding the President of the Transcend after the Battle of New Canaan.
In The Empress and the Ambassador, Empress Diana has the Impera Protego (dog-Latin for "Imperial Protectors"), since the Scipio Empire uses a Space Romans motif. She's actually Genre Savvy about it, fully aware that the historical Praetorians often mounted Military Coups against the emperor, as the Impera Protego indeed attempts over dislike of her newly inked alliance with the Transcend.
Good. The salt of the earth like their liege, they are shown relaxing while off duty, laughing and talking about their families to show they're nice. Assuming they have to arrest the heroes, they're apologetic, though also not easily escaped as they are quite diligent about their duties.
Bad. They will seem like good King's Men at first, but their inner natures are revealed through nasty swearing and messy quarters. When ordered to arrest the heroes, they'll beat them up in doing so even if it's unnecessary. If the heroes are sent to be tortured, these King's Men are pleased about it. They'll ask to watch too.
In Gaunt's Ghosts, the Suicide Kings, an elite unit within the titular regiment, draw their name from the royal guard of the High King of Tanith (the regiment's lost homeworld), the Nalsheen. If the High King was in danger, the Nalsheen would shield him with their own bodies and were armed only with knives because swinging larger weapons at that range might injure the king by accident. In exchange for the fact that their lives could end at any moment, the Nalsheen enjoyed the same absolute authority as the High King himself, and so got the nickname "Suicide Kings".
In The Dinosaur Lords, the Emperor of Nuevaropa is personally protected by the fanatical Scarlet Tyrants who have a rather bad habit of killing potential threats to the Emperor rather than taking them alive. That said, each is a highly skilled warrior who can often strike so quickly that it's difficult to see with the human eye.
In Christopher Ruocchio's The Sun Eater, the hostile alien Cielcins have an alliance with renegade human technologists. The Cielcins are already superhumanly strong and fast, but their Extrasolarian allies then create cyborg Super Soldiers from them, called Chimeras. The Chimeras have an adamant exoskeleton, further enhanced strength and speed plus a number of built-in weapons. Then there are 6 special Chimeras...these are the Vayadan. The 6 Vayadan are further enhanced (the first one encountered was 30 feet tall and a living siege engine that could tear through fortress walls) and directly serve the Cielcin's "King of Kings" as its bodyguard and generals.
In A Memory of Flames, the Speaker of the Realms has a group of "Adamantine Men" serving as their personal guard. The fanatically brave and loyal Adamantine Men also served the Realms by helping the Alchemists control dragons for the various Kings and Queens.
The Chronicles of Dorsa: The palace guards protect the Emperor/Empress and the royal family, while they also have black-clad guards as escorts when outside, with personal ones too. Joslyn is assigned initially to Tasia as the new member of the palace guard, and is her personal guard. The pair become lovers, and Tasia promotes Joslyn to lead the corps when she has become Empress. Linna also becomes a personal guard of Tasia's later.
made up of Vikings.