The Nobles in Wolf's Rain. They may not have a monarch, but they do have ridiculously overpowered technology to compensate.
We see a huge variety of these in Berserk, from King to Viscount. More often than not, they don't do too well or last too long, mostly if they get in Griffith's way.
Class struggles (of the Star-Crossed Lovers variety) are fairly important in Zero no Tsukaima, in which the nobility is largely (but not entirely) defined by being able to use magic.
The Armstrong Family from Fullmetal Alchemist have estates all over the nation, a legacy running back centuries and have entire families that have been in their service for generations. They're also a pack of Boisterous Bruisers and are, with one exception, all amazingly friendly. NOW WITNESS THE ARISTOCRATIC REFINEMENT THAT HAS BEEN PASSED DOWN THE ARMSTRONG LINE FOR GENERATIONS!!!
Austria from Axis Powers Hetalia. Liechtenstein also has shades of this in part due to being a Principality, not to mention being named after her ruling royals.
Black Butler has this all over the place, both bad (Such as Alois Trancy in the anime and Baron Kelvin in the manga) and good (well, to a point) examples, such as Elizabeth Middleford and, of course, Ciel Phantomhive himself.
Mobile Suit Gundam F91 also had an aristocratic family (the Ronahs) as the antagonists. This is at the heart of the Ronahs' belief system: that certain people are simply better than others, and it is the rightful place of the aristocracy to rule over the commoners. Though one does wonder what this says about them that their patriarch purchased their noble title, rather than inheriting it.
The central protagonists and antagonists of Hyakujitsu No Bara are all aristocrats from varying countries. Taki is the shinka of the Emperor and from the first of the Eight Branch Families, Katsuragi is from the second of the Eight Branch Families, Theodora is a Eurotean princess, and Klaus' family is nobility before the Western Alliance conquers their country.
Both played straight and referenced in Kaze to Ki no Uta. At one point Serge, in his Inner Monologue, remarks that he imagined Gilbert's blood would be blue. Interestingly, although many of the characters in KazeKi are blue bloods, Gilbert is not really one of them, so it's not entirely clear what exactly Serge (who is himself a Viscount) was alluding to here.
The Celestial Dragon World Nobles of One Piece are the Aristocrats Are Evil version of this quite heavily, having been given absolute freedom to do whatever they please to everyone beneath them (who is EVERYONE, even in this world where Asskicking Equals Authority is the norm), they abuse this freedom to the hilt. One decides on a whim to take a random guy's fiancee to be his own concubine, then shoots the guy when he protests.
The Dressrosa arc explains the Celestial Dragons a bit. The World Government was originally founded by twenty kingdoms, whose royal families were then invited to live in Mariejois, the capital of the WG. 19 of the royal houses were soon replaced by other, lesser nobles, such as the Riku family replacing the Donquixote family in Dressrosa. The only family who refused was the Nefertari family of Alabasta, who actually count more as The Beautiful Elite than Aristocrats Are Evil. Yes, this means that Vivi and Cobra are technically World Nobles.
There is only one exception to their nigh-unlimited freedom: no World Noble can ever permanently leave Mariejois and completely abandon their life as a Celestial Dragon, lest they be dubbed as "traitors". Which is why Donquixote Doflamingo was unable to rejoin the World Nobles after his father took his family out of Mariejois to live a normal life — much to his ire.
Code Geass possesses a good number of nobles. Most of them are Britannian, but we get to see a few former Japanese families and the Chinese elites at times.
In the Wild Series, Mikhail is both rich and very well connected.
The Nobles from Vampire Hunter D are a truly different breed from commoners, and have followed entirely different cultural conventions for thousands of years. Despite of their decline they command technology and magic far beyond what is available for ordinary people, and some have managed to cling to their lands and status despite of being universally reviled and feared thanks to this. Oh, and they are all vampires, ofcourse.
Used literally in Seiketsu no Hagurama. The Gadgeteer Genius prince is one of a group of people with blue blood at war with the red-blooded people. Part of the manga involves him discovering his machines being used to eradicate the remaining red-blooded refugees by his father.
Soul Society is split into commoners and nobility. Commoners are humans who died in the living world then entered Soul Society and live in an assigned district of the Rukongai. Nobles, on the other hand are those souls actually born in Soul Society. They tend to live in Seireitei and are significantly more likely to display officer-level shinigami power than commoners. There's also a major/minor nobility distinction, with older, more gifted families commanding greater authority. In the past, it used to be unheard of for the shinigami ranks to be made up of anything but nobility. Since Yamamoto reorganised the shinigami academy, however, more Shinigami have Rukongai origins and commoners have even occasionally made captain. There's still a stigma to common origins, however, and for at least one shinigami (Renji) the noble-versus-commoner issue was something he took personally.
The Quincy clan has a de facto nobility based on a "pure blood" vs. "mixed blood" distinction. Pure blood families like the Ishidas have mixed blood families as foot soldiers and servants, and traditionally the two do not intermarry.
Little Prince Cedie has its titular character for being the grandson of the Earl of Dorincourt.
My father was as brave a lord As ever Europe did afford; My mother was a lady bright, My husband was a valiant knight. And I my self a lady gay, Bedeckt with gorgious rich array; The bravest lady in the land Had not more pleasures to command.
Kal-El, aka Clark Kent aka Superman is a scion of the House of El, a noble family of scientists who in most continuities had much wealth, power, and influence over all of Krypton. Of course, it didn't stop all of Krypton from disbelieving Jor-El's prediction that Krypton would nuke itself. Supergirl is also a part of this family, being Superman's cousin, and Superman's clone Superboy was made an honorary member of the family by Superman. All three of them wear the Superman S, which is generally explained as being the House of El's family crest.
In Belle-Belle, the heroine is a nobleman's daughter. When the king orders every family of noble blood to fight for him or pay a high tax, she opts for Sweet Polly Oliver to deliver them. (So did her sisters. They couldn't pull it off.)
In Tattercoats, she is the granddaughter of a great nobleman.
In Catskin, the heroine is the daughter of a gentleman, and marries a young lord.
The main Klingon Defense Force protagonist averts this, given he's not even a Klingon. Brokosh is a Lethean mercenary and didn't find out that Ba'woV, daughter of N'Gara, of the House of Chel'toK was a noblewoman until after they'd started dating. However, Chel'toK, while still a Great House, is pretty minor: Their only holding of note is a nearly depleted section of asteroid belt, and while they do have a House Fleet, it consists of two Birds-of-Prey and an ancient D7 battlecruiser.
General K'Bor, son of QulDun, of the House of J'mpok plays it straight. He's one of the "old guard" Klingons and the uncle of J'mpok, the current chancellor.
A major plot point of the movie Penelope is that the titular character's curse can only be broken when a blue-blood declares he loves her. She ends up breaking the curse by stating that she loves herself the way she is, curse and all. Both heartwarming and amusing, as you find out that the man she loves and who presented himself as a blue-blood was actually lying, and when she begs him to just say he loves her and that he doesn't have to talk to her after that, he sadly responds that he can't, but not for the reasons she thinks (i.e. he finds her ugly due to the curse giving her a pig's nose, which actually isn't that bad)).
In Robin Hood (1991), Sir Robert/Robin is a Saxon noble, the Earl of Huntingdon, while Baron Daguerre and Sir Miles are Norman nobles.
The Vor in Lois McMaster Bujold's Barrayar, though they themselves claim they are a military caste, and not an aristocracy (which is exactly what aristocracy was in the Middle Ages). Most other people treat them like aristocrats.
Lord Boscastle in the Strangers And Brothers series is a REAL aristocrat, who can dismiss a mere Tudor parvenu with "I simply don't KNOW him." But he is all the more ready to befriend the likes of Roy Calvert; the gap between people he Knows and those he doesn't is so cavernous that it renders all other distinctions insignificant.
In Avram Davidson's "The Case of the Mother-in-Law of Pearl", Prince von Vlox, in his behavior and his references to the family's history (e.g., calling Paracelsus "Theo"), displays "an arrogance that transcended mere snobbery."
The novel appears to indicate that nobles are somehow better than regular folk. The Bene Gesserit are only shown caring about noble bloodlines in their quest to create a perfect being.
Most likely the noble bloodlines are "noble" because they've been subjected to the generations of manipulation by the Bene Gesserit, while the commoners don't have as well kept records of their genetic history, making them less useful for their plans.
The prequel novels also reveal that the Atreides were not originally nobility (Vorian Atreides being a created in a lab by his cymek father and marrying a barmaid) and do not show when they were first granted the title.
In First & Only and Ghostmaker, the Jantine Patricians and Volpone Bluebloods are quite scornful of the Ghosts.
In Necropolis, the hive's constitution is carefully written to divvy up power between the nobles so that there is no sovereign. And where, when the Ghosts are investigating their assigned and wretched quarters, they consider that the Volpone Bluebloods probably have nicer rooms.
In Sabbat Martyr they confront officials who don't let them use their flamer, because they are not of high enough birth.
There is a semi-sensible reason behind that last one though. On the planet in question, water is expecially scarce. Setting everything on fire may get out of hand. Of course, this being a full blown war...
Sandy Mitchell's Scourge the Heretic features such a stratified noble society that even an Inquisitor's agent does not realize how rude he has to be; a local explains that politeness will be interpreted as low status.
In Dan Abnett's Horus Rising, the Luna Wolves are scorned by various other Space Marines as base-born.
In William King's Space Wolf novel Grey Hunters, Trainor explains that he is an officer because he was born in one of the high clans. (He found fighting Chaos forces rather a shock after such conflicts as his planets had had before.)
In Mike Lee's Horus Heresy novel Fallen Angels, the representatives of the rebels are almost all nobles who have lost power and wealth because of the Imperium's control of their planet.
In Matt Farrer's "After Desh'ea" (in Tales of the Heresy), the "high-riders" which Angron holds in (justified) contempt, the targets of his Gladiator Revolt
In Ben Counter's Soul Drinkers novel Chapter War, Lord Sovelin Falken. At one point, he throws his weight around, pointing out that the governor is his great-aunt — but that's because he has vital information, and he has to use anything he can to get it through.
Susan Dexter's The Wind-Witch revolves about a widowed noblewoman's efforts to work her husband's estate for A Year and a Day — which will give her a claim to the land.
Jane Austen's works. Unlike the Regency Romance, while all of her characters are blue-bloods, only a handful have titles. Baronets, mostly, although Darcy is related to an earl who does not appear in the work.
A notable example as Darcy's name is clearly ripped off from the D'Arcy family, a genuine family of earls who, in the real world, had run out of male heirs about a century earlier; and his first name, Fitzwilliam, suggests strongly that his uncle is the Earl Fitzwilliam, a hugely famous and powerful man at the time. So much for No Celebrities Were Harmed...
Also interesting, particularly in Sense and Sensibility and Pride and Prejudice, is the tension (Truth in Television at the time) between the blue-blooded gentry who had somehow had their traditional incomes diverted away from them by being unable to inherit, or by their becoming worthless, and the rising commoner merchants (like Mrs. Bennet's family) who were often richer than them, but traditionally unacceptable as members of the blue-blooded clique.
In Northanger Abbey, the narrator, explaining why Catherine had not fallen in love before seventeen, lists several reasons. One is that there was no lord in the neighborhood, or even a baronet.
Edgar Rice Burroughs's heroes and heroines are Blue Bloods when not actually of Royal Blood — though this does cover upper-class Americans as well as titled characters, and the characters (and readers) may not be aware of it. Villains and other characters may also have it.
It took four men, all four ablaze with gorgeous decoration, and the Chief of them unable to exist with fewer than two gold watches in his pocket, emulative of the noble and chaste fashion set by Monseigneur, to conduct the happy chocolate to Monseigneur's lips. One lacquey carried the chocolate-pot into the sacred presence; a second, milled and frothed the chocolate with the little instrument he bore for that function; a third, presented the favoured napkin; a fourth (he of the two gold watches), poured the chocolate out. It was impossible for Monseigneur to dispense with one of these attendants on the chocolate and hold his high place under the admiring Heavens. Deep would have been the blot upon his escutcheon if his chocolate had been ignobly waited on by only three men; he must have died of two.
It was to be seen every day, for those aristos were such fools! They were traitors to the people of course, all of them, men, women, and children, who happened to be descendants of the great men who since the Crusades had made the glory of France: her old NOBLESSE. Their ancestors had oppressed the people, had crushed them under the scarlet heels of their dainty buckled shoes, and now the people had become the rulers of France and crushed their former masters—not beneath their heel, for they went shoeless mostly in these days—but a more effectual weight, the knife of the guillotine.
In G. K. Chesterton's The Return of Don Quixote, various noblemen are signficant characters; the hero Michael Herne falls in love with the Honourable Rosamund Severne. At the climax, he reveals that her family really are Smiths, with no claim to the title, though it breaks his heart. Later, he learns that she has changed her name to "Miss Smith" — and promptly goes in search of her.
His play Magic takes place at a Duke's house.
In the Father Brown story "The Mistake of the Machine", the story turns on an assumption that Lord Falconroy must come from an old family; in fact, he holds a newly created title and has — a rather interesting past.
Terry Pratchett's Discworld. Particularly in Feet of Clay, where the Dragon King of Arms meticulously traces noble lines and deplores how he must produce coats-of-arms for the low-born, and in the Tiffany Aching books, where the baron's son Roland, after a stint as a Royal Brat, is the only boy that Tiffany can talk to because all the rest are afraid to talk to a witch.
Ellen Kusher's Swordspoint and The Privilege of the Sword.
Sharpe meets a few. Among the more notable, obviously, is the Duke of Wellington, Sharpe's commander.
Others range from Peter D'Alembord — a classic Cultured Warrior and first-class infantry officer — to the Prince of Orange, whose incompetence as a commander is such that Sharpe personally shoots him half-way through a battle in order to reduce the slaughter.
In the Spaceforce novels, the powerful Taysan Empire is ruled by an absolute monarch with the backup of Imperial and Noble Castes. And one of the series' main characters, Jez, is a rare surviving member of the nobility of her homeworld, who governed the planet before her whole species was overthrown in a genocidal civil war.
In Kerry Greenwood's The Castlemaine Murders, the Honourable Miss Phryne Fisher's sister Eliza plays the disdainful Upper-Class Twit trope straight in the early part of the book - only to subvert the trope after Eliza finally tells Phryne why she was sent to Australia (she was acting out because of how unhappy she was).
Most of the main characters in George R.R. Martin's A Song of Ice and Fire are members of the nobility. The details vary: we have members of very old and powerful houses such as Starks and Lannisters, petty knights and barely-even nobles like the Cleganes, personally ennobled commoners like Davos Seaworth and everything in between.
In The Edge, the hereditary aristocracy are actually called bluebloods to distinguish them from the nobility, the bluebloods who have already earned their titles.
Purebloods fulfill this role in the Harry Potter series. Although the wizarding world lacks royalty or titles, most pureblood families enjoy a disproportionate amount of wealth, power, and influence. Most also have an aristocratic disdain for not-so-pure-blooded wizards and especially for muggles.
In Fanon most purebloods are royalty with titles even more if the are from the "Ancient and Noble familys" the Potters being one of them.
Virtually all of the major and minor characters in the Deryni works are in this class. The better ones treat members of the lowers orders (such as Revan in the Legends of Camber and Heirs off Camber and Morgan's pagan swordsmith Ferris from the story "Trial") quite well. The rest, well, see Aristocrats Are Evil.
Octavia sprang up, her white fists clenched, her eyes blazing and her figure quivering with outraged anger. "You would force me to play the trollop with this barbarian?" she exclaimed. "I will not! I am no market-block slut to smirk and ogle at a steppes robber. I am the daughter of a Nemedian lord—" "You were of the Nemedian nobility before my riders carried you off," returned Jehungir cynically. "Now you are merely a slave who will do as she is bid."
In Gene Stratton Porter's Freckles, Angel is a blue-blooded American with "ancestors reaching back to Plymouth Rock, and across the sea for generations before that." Freckles himself turns out to be the grandson of a nobleman. Though it gets less play, McLean was the son of a prosperous Scottish shipbuilder, though he made himself in the lumber trade.
In Gene Stratton Porter's Michael O'Halloran, Minturn, having gotten control of his sons after his wife made them into Royal Brats, knows it will be a long slog, but has hopes because they are "handsome little chaps with fine bodies and good ancestry".
Hugh, Viscount Trimingham, in The Go-Between. He is intelligent and likeable, though disfigured by a war wound, and takes his responsibilities to his tenants seriously. Much good it does him.
In Poul Anderson's Time Patrol story "Delenda Est", Deidre — she has an estate she can bring Everard and Van Sarawak to when making their imprisonment less onerous.
In one of the oldest surviving Robin Hood tales, Robin carefully inquires of the sorrowful knight whether he was a newly created one, finding out he is of Blue Blood before he helps him. Robin himself is a yeomen then and for centuries after, but in the Elizabethean to Victorian times, he became, often, a disinherited earl. Maid Marian, likewise for centuries a shepherdess, also became a frequent noblewoman then. In the 20th century, Robin went back to yeoman, for a Rags to Riches rise, but Marian still is often noble.
Pretty much all the protagonists in Tales of the Branion Realm — the ones that aren't are either royalty or end up raised to the nobility.
Like so much else in the Wheel of Time, just about every shade of this trope is present in one nation or another. Amongst the main characters, Moiraine, Elayne, Faile, Talmanes, Rand of house Mantear by virtue of his mother, Tigraine, the former daughter-heir, and eventually even Mat, Prince of Ravens and Perrin Goldeneyes, Lord of the Two Rivers as Steward for the Dragon Reborn.
There are examples of true badasses such as the Queens of Andor, many of whom lead troops both historically and contemporaneously. In the Last Battle, Elayne even gets an assist with a sword, despite having the One Power.
There are also examples of worthless, scheming layabouts, such as Tairens and Cairhenians.
In Dorothy Gilman's The Clairvoyant Countess Madame Karitska is technically a countess. Given that she was a small child when her family escaped the Russian Revolution, it doesn't mean much to her.
In Poul Anderson's "Time Lag", Elva's husband is the Freeholder, which position has both the authority and duty to pass judgment. Elva can represent him partly because her own family holds a similar position. At the end, she learns her son holds the position , having survived the attack.
In Andre Norton's Catseye, Tikil is a luxury port, catering to the wealthy high-born who vacation there. Kyger's animal shop is one such store.
In Honor Harrington, the Star Kingdom of Manticore has a noble class that was mostly descended from the first wave of colonists. However, they also create new peerages for exceptionally distinguished commoners, such as the protagonist herself.
Most Manticoran nobles (including the royal family) are driven by a strong sense of noblesse oblige, and recognize that an inherited title doesn't make them automatically better that commoners; those that don'tnote cough Conservative Association cough tend to dive headlong into Aristocrats Are Evil territory.
In Bess Streeter Aldrich's A Lantern in her Hand, the (dead) father had been an aristocrat who married beneath himself in Ireland.
Kindling Ashes: Corran is the youngest son of the noble Dunesdale family. This causes problems in his relationship with Tilda because his dad doesn't want him marrying a commoner.
Live Action TV
Downton Abbey provides a huge variety of examples from the British peerage; Earls (Lord Grantham himself), Marquesses (Shrimpie Flintshire), Dukes and Duchesses (the Duke of Crowborough and the Duchess of Yeovil), Baronets (Sir John Bullock), Viscounts (Anthony Foyle), Esquires (Matthew Crawley) and even King George V in the 2013 Christmas Special.
More subtly, but Commander Spock from Star Trek: The Original Series. Not only is his father a very respected diplomat, but his extended family owns a great deal of land and includes T'Pau, one of the most influential people on Vulcan.
Worf comes from an ancient, extremely high-profile family that automatically places him at the centre of rather a lot of Klingon intrigue (and enable no end of episode plots). Most of the other named Klingons in the series are also aristocrats.
Trust me, Clara Vere de Vere, From yon blue heavens above us bent The gardener Adam and his wife Smile at the claims of long descent. Howe'er it be, it seems to me, 'Tis only noble to be good. Kind hearts are more than coronets, And simple faith than Norman blood.
Finian: Don't you realize, lad, Sharon is from quality stock? Why, her whole family tree for generations back consists of nothin' but ancestors. Woody: We've been descendin' a long time too. Finian: Ah, but how long? Sharon's grandparents go back to the dawn of history. Blue-blooded amebas they were, with a dauntless ambition. Up they came through the paleozoic slime — from ameba to tadpole, from tadpole to daffodil, from daffodil to dromedary, and from dromedary to McLonergan. That's the background Sharon comes from — so get along with your luggage, lad, you haven't a chance.
In Oscar Wilde's The Importance of Being Earnest, Lady Augusta Bracknell has a very acute sense of who is a blue blood and who isn't. She refuses to let her daughter Gwendolyn marry Jack Worthing when she discovers that he was adopted by his upper-crust guardian, who found him as a baby in a handbag at the train station.
In Of Thee I Sing, President Wintergreen gets the United States into international difficulties with France when its ambassador discovers that Diana Devereaux (who was to have been the President's wife if he hadn't met Mary Turner) is the illegitimate daughter of the illegitimate son of the illegitimate nephew of Napoleon.
I am, in point of fact, a particularly haughty and exclusive person, of pre-Adamite ancestral descent. You will understand this when I tell you that I can trace my ancestry back to a protoplasmal atomic globule. Consequently, my family pride is something inconceivable. I can't help it. I was born sneering. But I struggle hard to overcome this defect. I mortify my pride continually. When all the great officers of state resigned in a body, because they were too proud to serve under an ex-tailor, did I not unhesitantly accept all their posts at once?
This trope is invoked and parodied throughout Iolanthe, where the self-confessedly mostly brainless yet immensely wealthy, powerful, and refined members of the House of Peers find their marriage proposals to the beautiful commoner Phyllis scorned, and their legislative powers subverted by supernatural fairies.
There are two prominent examples in the Soul Series — Lady Isabella "Ivy" Valentine is the daughter of the Earl and Countess Valentine, and her stages nearly always feature her enormous family house. The other example is Frenchman Raphael Sorel, whose title is not specified, but he is noted to be a noble.
Mystics in Sa Ga Frontier both in the aristocratic sense and the literal sense.
If the lord in Fire Emblem doesn't have Royal Blood, they'll be nobility. Examples include Sigurd, Roy, Eliwood, Hector, Lyn, and eventually even Ike.
Though this doesn't apply to every lord, there's a helpful rule of thumb for most of them: blue hair = blue blood.
Archadia of Final Fantasy XII is very based around hierarchy. Besides the noble houses, which can mix this with Royal Blood, there's also the Gentry, who tend to look down on commoners. There's also an intermediate class, which tend to behave fairly close to trope too.
Dragon Age: Origins has got a hierarchical system of nobility loosely based on that of England, with Teyrns (Dukes), Arls (Earls), and Banns (Barons) in that order of status. Dwarves have also their own caste system, where the members of upmost caste are either ridiculously rich or belong to a noble family. (And then there's Paragons, but let's not go there...)
Interestingly enough, the Banns are technically just a noble(wo)man who has a number of freeholds sworn to it. The peasants are free to chose whoever they want to be their Bann and can change allegiance whenever they want, which can lead to age long feuds between family's of Banns, ex-Banns and aspiring Banns. Most people just goes with the same lord as their parents did, as his castle and soldiers are usually the closest, any threatens of what said soldiers might do if their Lord don't get enough votes are left unsaid.
The icon for the Human Noble origin is a drop of blue blood with a crown over it, since they are the younger child of a Teyrn.
Deus Ex Icarus Effect: Lucius describes himself as a "scion of blue bloods from the old country" in the book's prologue.
In Star Wars: The Old Republic, Alderaan is in a terrible mess due to the untimely death of the Queen and her heir, plunging the planet into a free-for-all civil war among about a half-dozen houses of these. The main issue is that the rather crazy head of House Ulgo has usurped the crown, declared the planet's independence, and started destroying the other noble houses. Seeing as about half the surviving houses support the Republic (including House Organa), whereas the Empire is backing their rivals House Thul (who started as merchants and earned their lands and titles), the planet becomes a miniature version of the whole galactic war.
The Order of the Stick: Particularly those of Azure City, where giving a title to two war heroes garners objections.
Later, Vaarsuvius elects to simply murder a villain with this background, instead of bothering to denounce him publicly. It's a pretty effective solution.
The Zahard family and the 10 supporting families in Tower of God. They are indeed special, since only they are by birth able to wield Shinsoo immediately, as their families have special ties to the power-granting Guardians.
In Homestuck, the Trolls have a caste system based around the color of their blood. While the trolls with blue blood aren't quite at the top, they seem to be the only ones who care very much about where anyone ranks, and as such they lord over those in lower castes and demand those in higher castes lord over them.
However, it's unclear if all members of the blue-blooded castes do this, or if it's just Equius and his, er, strange tastes.
Additionally, Snowman has blue blood, and is formerly known as the Black Queen.
By contrast, Twilight Sparkle and her brother, Shining Armor, earned their way into the top tier of Equestrian nobility with Twilight being the personal protege of Princess Celestia and Shining being Captain of the Royal Guard, the Prince Consort of Princess Cadence and Co-Governor of the Crystal Empire. By the end of season 3, Twilight becomes an Alicorn Princess.
The nobility in the Real Life is usually divided in untitled nobility (i.e. noblemen whose status implies servant status to either a superior noble or to state), including gentlemen, esquires and knights and titled nobility, also known as "peerage", i.e. land-owning nobility. Those would be baronets, barons, earls, viscounts, marqueses, counts and princes. The highest ranks of the nobility, such as Dukes, Grand Princes and Grand Dukes, would imply Royal Blood instead of just Blue Blood.
In the Middle Ages, nobility implied exemption of taxes - and duty to serve as a soldier. That is due to Feudal system. There were no standing armies, but the soldiers (knights and men-at-arms) were expected to train on their own and acquire their own armour and weapons. Exemption from taxes implied that the nobleman would spend all his income on weapons, gear and practising martial skills. Usually the core of the feudal army would be supplanted either by mercenaries or conscripted commoners (arriere-ban).
Depending of the country, the nobility would consist of 1% (France) up to 20% (Hungary) of the populace. The greater the likelihood of the state being involved in warfare, the more noblemen there would also be.