The Cauldron Born
Some of the most notable cuts include the scenes of the Horned King's undead army, the Cauldron Born, killing some of his henchmen (after two are pounced upon, the men dissolve in a very graphic manner in which their skin bubbles and melts off their bodies, leaving a pair of skeletons behind). Another notable scene that was cut was that of a man's throat being slashed with a sword. Both cuts caused jumps in the soundtrack.
Recently, some production cels of the melting men were obtained during an online auction, and a couple of years later these cells were inserted into footage of the released film (along with some missing shots featured in the trailer), which was then published on YouTube to show how the scene might have looked in motion.
Producer Joe Hale is said to own the fully black and white uncut version of the film, though he has never released these aforementioned (or any other) deleted scenes to the public. It has also been theorized that the lost scenes may currently be stored somewhere at either Walt Disney Animation Studios, or Disney Studios (both located in Burbank, California), although this has never been proven as anything more than speculation.