Jaws
Terminator
Halloween
Psycho
Mad MaxThere’s also been examples such as Grease and Scarface where although the original mixes were not mono they still were given 5.1 remixes later on that completely revised everything.
though fortunately for at least most of these movies the original mono/dolby mix was provided alongside the 5.1 version on their blu ray releases (Terminator being the only exception), though for Grease the original Dolby mix finally resurfaced in 5.1 form on the recent 40th anniversary release
It was based off an original six track mix which I believe was only used in a preview showing. The general release had a two channel stereo mix.
Additionally some BD releases of Halloween and Mad Max have mono tracks that are actually downmixes of the surround track. The recent UHD release of Halloween sadly is one of them.