Blue Velvet (1986 Film, Formerly Missing Deleted Scenes)
In 1986, two years after the massive failure that was his adaptation of David Herbert's Dune, filmmaker David Lynch rebounded by releasing what is arguably his greatest film, Blue Velvet. Taking place in the fictional town of Lumberton, USA, Blue Velvet is a noir about a young man named Jeffrey Beaumont who discovers a severed ear in a field. This discovery leads to him crossing paths with the dark, violent underworld of this seemingly idylic town.
Lynch was contractually obligated to create a film that ran two hours long. The theatrical version fulfilled that - in fact, it is only a few frames under two hours. However, Lynch shot four hours of footage that contained many subplots and characters. Among them were Jeffrey's college girlfriend, additional scenes with Sandy's boyfriend Mike, and an explanation as to how the ear ended up in the field.
For many years, these scenes were thought to be missing forever. Lynch had tried to locate them, but the production company had gone bankrupt and no one knew where the footage had been stored. The 2002 special edition DVD included reproductions of the deleted scenes using stills and photographs that had been previously published in a variety of film magazines. This was thought to be as close as fans of the film would ever get to the scenes.
Before the Blu-Ray was released in 2011, Lynch revealed that the missing scenes had been found "somewhere in Seattle" and would be included in the new release. 
The scenes were released as a 52-minute mini-movie that includes production credits. Various websites have broken down the content of the scenes. 
Certain scenes have ended up on YouTube, but every time the complete 52-minute compilation gets uploaded it gets deleted. However, the Blu-Ray is still in print and easily accessible to those who would like to see the lost scenes.
Upon its release, the Blu-Ray was widely praised with many pointing to the deleted scenes as a highlight.