Metafictional Title

The Namesake of a story can be all kinds of things, a person, a symbol, a weapon. Sometimes, in just a touch of meta-fiction, The Namesake is a book within the book. Sometimes, as in The Way of Kings, this is a holy book. Sometimes, as in The King in Yellow, it's a distinctly unholy book. In any case, it's very important in some way to the story, although how is not always clear at first.

Comic Books

 * Marvel Comics published Darkhold: Pages From the Book of Sin in which a group of heroes tried to locate the lost pages of the eponymous Darkhold. (The Drakhold is basically the Marvel Universe's equivalent of the Necronomicon.)
 * The Krypton Chronicles was DC Comics mini-series exploring Superman's ancestry. In it, Clark kent is commissioned to write a book about Superman's ancestors called The Krypton Chronicles.
 * Similar to The Krypton Chronicles was The Atlantis Chronicles, which explored Aquaman's ancestry through The Atlantis Chronicles, the collected archives of Atlantean Royal Historians.
 * Marvels is about a Muggle Daily Bugle photographer named Phil Sheldon, who documents the activities and reputations of the Marvel Universe's superheroes. Near the end, he publishes a book called Marvels.

Film Live-Action

 * The Evil Dead was originally named Book of the Dead after the book of the same name, which appears in the movie. The name was changed because the executives didn't want people to think it was a movie about a book.
 * Raising Cain gets its name from the book that main character's father wrote while experimenting on him.

Literature

 * The Book of Three: A magical book that serves as a Macguffin for the story.
 * The City and The City
 * Cryptonomicon: Inside the story, the Cryptonomicon is a comprehensive study of cryptography, both for making and breaking codes.
 * The Hitchhiker's Guide to the Galaxy: The most important reference work for any hoopy galactic traveller. The entry for Earth consists of "Mostly Harmless".
 * House of Leaves
 * Infinite Jest: The Fictional Document is, in this case, a film so mesmerizing that the U.S. government is interested in weaponizing it.
 * The King in Yellow: A play that when read or performed, drives the audience violently insane.
 * The Manual of Detection: The book in question is a handbook for the detectives of The Agency.
 * The Neverending Story.
 * Pale Fire
 * The Real Inspector Hound by Tom Stoppard is a play about two theater critics watching a production of The Real Inspector Hound.
 * So You Want to Be a Wizard is the first book in the Young Wizards series, and also a title of the main character's wizards' manual that appears in it. Later books in the series imply that the fictional book looks like a real-world book to anyone unauthorized tries to read it. In the same series, Book Of Night With Moon.
 * The Robert Rankin novel The Suburban Book of the Dead: Armageddon III: The Remake is named after The Suburban Book of the Dead, a religious tome within the book ... but which turns out not to be the same Suburban Book Of The Dead that appeared in Armageddon: The Musical.
 * Also by Rankin, The Book of Ultimate Truths, the first novel in the Hugo Rune/Cornelius Murphy saga, is named after Rune's greatest work.
 * The Twilight of the Vilp by Paul Ableson is about the surreal misadventures of a novelist attempting to write a novel titled The Twilight of the Vilp.
 * The Way of Kings: The book is something between a holy book, philosophy, and a chivalric code.
 * The Malazan Book of the Fallen

Live Action TV

 * Pulaski (a.k.a. Pulaski: The TV Detective) was series about Larry Summers, an actor who plays the title character (a former priest turned PI) on the Show Within a Show Pulaski, and who keeps getting caught up in adventures that would be more appropriate for the character he plays.

Video Games

 * The Elder Scrolls

Webcomics

 * A Beginner's Guide to the End of the Universe
 * The Art of Domination
 * The Hero's Handbook