Meaningful Release Date

""You are PSYCHED about this SPECIAL DATE, 11.11.11 ... a date exhibiting just the sort of numerical gimmick corporations love to exploit for their big releases, or for launching MAJOR REBRANDING INITIATIVES.""

- Homestuck

This is when some movie, game, TV show, etc., comes out and its release date has some referential meaning related to said media being released. This is usually simplt gimmicky, though the date may be relevant to the plot.

Horror movies particularly like to come out on Friday the 13th, as it's an unlucky date, but then, any holiday is a good time for a horror movie.

Note: Being released on a repetitive date such as 11/11/11 or 12/12/12 does not make it an example, unless the number being repeated is an Arc Number.

Anime

 * It's not entirely clear if this is intentional, but the last two episodes of Mahou Shoujo Madoka Magica were released on Good Friday; and in the finale
 * Interestingly, the series finale was one week before April 30th/May 1st. Walpurgis Night; the name of the "end boss."
 * Note that the last two episodes were delayed for several weeks - not because of this trope, but because of a horrific natural disaster that occurred shortly after Episode 10 came out.

Comics -- Books

 * A Superman graphic novel titled End of the Century, featuring a massive conflict involving Lex Luthor and the title character, was about and was released as close to the last week of December 1999 as possible. An unrelated story in the regular Superman comics around the same time was the Y 2 K arc, which also took place on that day and starred Superman and Lex Luthor.

Film

 * The movie Nine came out on September 9, 2009 (9/9/09).
 * Numerous horror movies tend to be released on Friday the 13th, particularly Dracula (1931) and the Friday the 13 th movies.
 * The remake of The Omen was released on June 6, 2006 (6/6/06).
 * And before that, the original was sneak previewed nationwide on June 6, 1976 (the official date was June 25th). Which also happened to be a Sunday.
 * Independence Day was originally scheduled for release on July 3; subverted in that public anticipation did lead to some showings on the 2nd, however.
 * The Film of the Book Nineteen Eighty-Four came out in 1984.
 * Some of the scenes were deliberately filmed on the dates given for those events in the book (even though Orwell makes it clear those dates were just Winston Smith's guesses in the first place).
 * In Disaster Movie, the world is set to end on August 29, 2008 -- the very same day that the film opened in theatres.
 * Fantastic Four was originally supposed to be released on July 4, 2005, and early trailers played this up. However, its release date was shifted to four days later.
 * The Number 23 opened on February 23, 2007.
 * The remake of Black Christmas opened in the US on December 25, 2006. The UK got it ten days earlier, on December 15th.
 * The remake of The Mechanic opened on January 28, 2011, the same day that the film's climax takes place.
 * Averted in the case of V for Vendetta, which was originally scheduled to open on November 4, 2005 (the day before Guy Fawkes Night/the 400th anniversary of the Gunpowder Plot) but was delayed four months due to Warner Bros. being unsure about its box office prospects.
 * In addition, there had been terrorist bombings in London, so.....
 * Titanic will be re-released in 3D in 2012, the 100th anniversary of the sinking.
 * 10th James Bond (007) movie The Spy Who Loved Me was released on July 7, 1977.
 * Childs Play opened on November 9th, 1988, which is also the day when Charles Lee Ray becomes Chucky in the film.
 * The film 11-11-11 opened in... guess it.

Literature

 * The 13th and final installment of A Series of Unfortunate Events was released on Friday, October 13. The word "thirteen" appeared on virtually every page of the book.
 * One of the hints that George Orwell's Nineteen Eighty-Four is an allegory for contemporary politics is that its title is an altered version of the year of its writing -- 1948.

Live Action TV

 * In the fifth season of the revived Doctor Who, the date in which the universe was scheduled to blow up was June 26th 2010, the day the last episode of that season aired.
 * April 22, 2011 at 5:02pm was the date . Accounting for Lake Silencio timezones vs. British timezones, this means that the day "The Impossible Astronaut" aired.
 * This happened by accident, but the 28th episode of Kamen Rider OOO and the thousandth episode total of the series aired on April 3, 2011, 40 years to the day since the series began airing on television.
 * By chance, the episode of Merlin which featured King Arthur pulling Excalibur out of the Stone was broadcast on Christmas Eve, 2011. According to Arthurian Legend, Arthur pulled the Sword in the Stone out of its anvil on Christmas Day.

Music

 * The remastered albums of The Beatles were released on 09/09/09.
 * Pink Floyd guitarist David Gilmour deliberately released his latest solo album, On An Island, a rumination on family life, aging, and mortality, on March 6th, 2006, the date of his 60th birthday.

Video Games

 * The demo for Sonic Generations was made available on June 23, 2011, exactly 20 years after the first Sonic the Hedgehog was released. This is fitting, as it's a game about Sonic's history.
 * Sonic 2 was released on November 24th, 1992, which was a Tuesday. Sonic Adventure 2 was also released on a Tuesday. Not only is it a pun, Tuesday is the second day of the week if you consider Sunday the 7th.
 * Sonic Generations's second demo was released on the 17th anniversary of Sonic & Knuckles.
 * The English patch for Yousei Daisensou was released on September 9. The game stars Cirno, who has a memetic association with the number 9.
 * Much like the above-mentioned 9 and Beatles remasters examples, The Beatles: Rock Band saw release on 09/09/09.
 * Ni GHTS Journey Of Dreams was announced on April 1st, 2007 and released in December of the same year. The series is known for having special events occur on Christmas Eve and April Fools Day.
 * The english release of Blaz Blue: Continuum Shift was July 20, 2010. 7/20 alludes to the 720-degree motion in fighting game terminology used for super versions of most command grab special moves.
 * All but one of the God of War video games have been released in March, the month named for the Roman God of War, Mars.
 * In addition, God of War III was released March 16. This may be a reference to John 3:16 in the Bible, as the series has some possible Christian overtones, III most of all.

Webcomics

 * Homestuck: The first page went up on April 13, or 4/13. Since then, the comic has used 413 as an Arc Number all over the place. Given the way Hussie's been writing by the seat of his pants, and that he had originally tried to launch the story on April 10, it's safe to assume he built the arc number around the launch date rather than vice versa.
 * Also, various anniversary animations have been released on 4/13, on the 413th day, and on similar dates based on the second Arc Number 612.
 * The second Arc Number is also a significant release date; Act 5 (where the number is introduced) began on June 12th, or 6/12.
 * The end-of-Act 5 animation, in which the universes of the kids (Arc Number 413) and the trolls (Arc Number 612) was released on October 25 (10/25, i.e. 4/13+6/12). Apparently this was a happy accident; Hussie had finished the video a little earlier, but it was close enough to the date that he decided to delay it.
 * Act 6 began on November 11, 2011, so Hussie lampshaded it by making it an in-universe meaningful release date, referred to as "2x3prong Day (whatever that means)". Not surprisingly, Act 6 introduces a new Arc Number based around four ones (11/11) or six ones (11/11/11), more commonly the latter.