Joystiq

The printed word
Starting point: While writing dates back to antiquity, we're starting the "industry" with the completion of Gutenberg's printing press bible in 1456.
Forty years later: By 1496, printing presses had been established in major cities across Europe, and advances such as color printing and engravings were adding some pizazz to the mass-produced written word. However, there are still more advances to come -- it will be five years until italic type is introduced and over 100 years until the first newspaper is printed.
Sources: 1, 2

Recorded music
Starting point: While music is possibly as old as man himself, recorded music started with Edison's invention of the phonograph in 1877.
Forty years later: In 1917, Woodrow Wilson had just declared "The Star Spangled Banner" to be the national anthem. Classical music is still popular, but recordings of vaudeville and ragtime hits are beginning to establish themselves in the popular culture. "Livery Stable Blues", which is often said to be the first jazz recording, is released in 1917.
Sources: 1, 2, 3

Comic books
Starting point: While the idea of matching words with pictures is at least hundreds of years old, American comic books probably date back to 1897's bound newspaper strip collection The Yellow Kid in McFadden's Flats.
Forty years later: In 1937, the so-called golden age of comics is just beginning. The first issue of Detective Comics is introduced by a company that will later be known simply as DC. Superman's debut in Action Comics is still a year away, and Dr. Fredric Wertham's famous assault on the comics industry won't start for over a decade.
Sources: 1, 2, 3

Film
Starting point: Edison's commission of the first motion picture camera, the kinetograph, in 1889.
Forty years later: In 1929, integrated soundtracks were still new to film. Disney's landmark animated short Steamboat Willy had only been around for a year, as had the Academy Awards. Landmark pictures like Gone with the Wind, Citizen Kane and Casablanca were a decade or more away. Theaters sell 90 million tickets a week nationwide in 1929.
Sources: 1, 2, 3

TV
Starting point: Philo Farnsworth's first experimental transmissions at Washington D.C.'s Jenkins Labs in 1923.
Forty years later: In 1963, over 87 percent of homes have a TV set, but less than 3 percent of homes have a color set. The nation is glued to 30+ straight hours of coverage devoted to president Kennedy's assassination and CBS and NBC extend their nightly newscasts to 30 minutes. Dr. Who starts its original run on the BBC, while popular American shows include The Flintstones, The Andy Griffith Show and Mister Ed. The first videotape recorder was introduced in 1963 for the low, low price of $30,000.
Sources: 1, 2, 3, 4, 5

Video games
Starting point: Ralph Baer's creation of a Pong-style "Brown Box" in May of 1967
Forty years later: Games have advanced technologically from abstract black and white lines and dots to 3D, high-definition virtual worlds. The industry generates sales of $12.5 billion per year and massively multiplayer games like World of Warcraft attract more than 8 million subscribers worldwide. Game consoles are in roughly 40 percent of American households with a TV set. Sixty-nine percent of heads of households play games, and the average game buyer is ... 40 years old!
Sources: 1, 2, 3, 4