Magic Librarian

""What do you think of the library?"

"It's pretty big," I murmured, looking all around me.

"Two hundred miles in every direction," said the Cat off-handedly and beginning to purr. "Twenty-six floors above ground, twenty-six below."

"You must have a copy of every book that's been written," I observed.

"Every book that will ever be written," corrected the Cat, "and a few others besides."

"How many?"

"Well, I've never counted them myself, but certainly more than twelve.""

- Lost in a Good Book

Books and libraries in fiction can be mystical things; keepers of information, certainly, of secrets and sometimes of magic, as well. It's natural, therefore, that some authors like to spread some of that magic onto the librarian, too--when they aren't making them hot or scary, that is. A magic librarian will very often have the ability to send readers (or people who either don't read or disparage books, to teach 'em a lesson) into the world within the books, and sometimes, pity those who don't return their books to the library before the due date.

Anime

 * Lilith and Eve, the two dimension-hopping witches in Yami to Boushi To Hon no Tabibito, happen to be librarians of a Magical Library, who are both magical and hot.
 * Yuuno Scrya of the Lyrical Nanoha franchise. Mage scholar, ferret changeling, and head librarian of the Infinite Library, partly thanks to his mastery of spells that let him scan through several books at once.

Comics

 * Lucien in The Sandman, who maintains the Library of Dream, which contains every book anybody ever thought or dreamed about writing, from the masterpieces of great authors who died before committing them to paper, down to the novel you always tell yourself you'll write one day. (The Bestselling Romantic Spy Thriller I Used To Think About On The Bus That Would Sell A Billion Copies And Mean I'd Never Have to Work Again. Not exactly the catchiest of titles, is it?) He knows everything about every book in the library, including where each of them is at any given moment, although at one point he admits that this comes at the cost of not being able to remember most things that happen outside the library, including who he was before he became the librarian.
 * The Doctor Who Magazine comic, for an explicit homage to The Lion the Witch And The Wardrobe, casts the Doctor as one for an extended fantasy sequence that takes almost an entire strip.

Film

 * Karl Konrad Koreander, of The Neverending Story, who kept the eponymous tome in his shop until Bastian stole it. Originally a fairly ordinary old book seller, the film series added implied magical properties (he can appear and disappear at will, apparently), and in the much-maligned third film he works as a librarian at Bastian's high school.
 * The Pagemaster is all about this trope.

Literature

 * Our page quote: in Thursday Next, the Cheshire Cat manages the Great Library, a magical place that contains all books that have been or will be written, and claims to know everything there is to know about them, including how many times they've been read, how many of them are being read at any given time, and by whom.
 * The Librarian of the Unseen University in the Discworld series. He's a wizard, and the library is attached to a wizards' university, but he also commands magics that come from the mere fact of it being a library (most notably the secret of L-Space, which connects every library that ever existed). He was also transformed into an orangutan, and decided to stay that way.
 * Oook.
 * In Kelly Link's short story Magic for Beginners, there's a whole TV show of magic librarians, and the entire television series the characters are watching (and, it's implied, also a part of themselves) takes place within a giant library.
 * By virtue of being staff at Hogwarts alone, Madame Pince from Harry Potter. She's also a Scary Librarian; Hogwarts library books have protective spells on them as a matter of course, but she's been known to add personal touches. Dumbledore mentions that absentmindedly doodling in the margins once caused a book to beat him violently about the head.
 * Garth Nix's The Old Kingdom series is full to the brim with these:
 * The Clayr, a large and clairvoyant group of people, have a massive library that houses not only normal books, but enchanted ones, grimories for creatures that may or may not exist, tombs of ancient beings that if let out will attempt to kill anyone they come into contact with, and, somehow, a figurine that  In a world full of shambling corpses, devious necromancers, and corrupt royalty, the library of the Clayr is probably full of the most frightening and dangerous people and artifacts.
 * The main character of the second book, Lirael, is a Second Assistant Librarian for the Clayr, and regularly not only completes her normal duties as a librarian, but runs around the extremely dangerous forbidden areas at night with a magical talking dog that she somehow created, breaking into locked chambers and reading ancient books.
 * Molly Moon is introduced to hypnosis by the local librarian, Lucy Logan.
 * In one of the Bailey School Kids books, the librarian is implied to be Merlin.
 * Craswell Crabbit in Terry Brooks' A Princess of Landover is a villainous version of this.

Live Action TV

 * Obligatory Buffy the Vampire Slayer example: Giles has to be one. Sure, he's not a magician himself per se, but then there was that whole stint when he was Ripper...
 * The librarian of the magic school in Charmed is magical, just like the rest of the cast. The first librarian we see is a disgruntled troll that keeps burning books.
 * Evil version: "Files & Records" at Wolfram & Hart in Angel, who has no name and can mentally search the entire content of the firms archives, apparently projecting the results onto her eyeballs.

Tabletop RPG

 * Yves, Archangel of Destiny in In Nomine. He collects all knowledge in his Library, including the memories of everyone who has passed on.
 * His Evil Counterpart, Kronos, Demon Prince of Fate, knows the location of everything in Hell's Archives. Unlike Yves, Kronos doesn't have access to all knowledge, but he does have access to all of Hell's official records.

Video Games

 * Patchouli Knowledge of Touhou Project is the Scarlet Devil Mansion's resident witch, and the de facto librarian of the place. She's constantly seen with a book in her hand when fighting, to top things off. Oh, and her debut stage theme is called "Voile, the Magic Library."

Web Comics

 * Phix of Wapsi Square is definitely a magic librarian. She's a (the?) sphinx.

Web Original

 * Derek the Bard, of Warning! Readers Advisory, is a wizard and keeper of the Greatest Library in the World.

Western Animation

 * Wan Shi Tong, the librarian of the titular library from (you guessed it) "The Library" episode in Avatar: The Last Airbender is some kind of ancient owl spirit that keeps irritating humans out of his domain.
 * In Courage the Cowardly Dog ("The Pixie and the Pickle Pirate"), a Scary Librarian curses Eustace and Muriel when they don't return a book on time, causing them to gradually transform into the characters from said book until Courage can return it to her.
 * Twilight Sparkle in My Little Pony Friendship Is Magic