If there was any more evidence needed to show that The Dark Knight is the biggest superhero film ever made, it has now been provided. According to The Hollywood Reporter, Apple reports that The Dark Knight is the best-selling movie download of 2008 on iTunes - which is especially notable since the film isn't available for purchase yet.

It seems like fans have pre-ordering the film for purchase and rental at such a rate that it has surpassed Disney's WALL-E as the year's top download.

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The film becomes available for purchase on iTunes and on DVD/Blu-Ray on Tuesday, December 9, 2008, just in time for the holiday season. The Dark Knight stars Christian Bale, Heath Ledger, Morgan Freeman, Aaron Eckhart, Gary Oldman and Maggie Gyllenhall. Directed by Christopher Nolan, the sequel to Batman Begins quickly became the highest grossing superhero film in history, and is second only to Titanic in overall sales.