The first that comes to mind for me is The Breakfast Club and I hope it never does have a sequel or remake
The Princess Bride is another good one
Edit: another one of my favourites is Wall.E, my favourite Pixar movie. There are also several other Pixar movies that don’t have sequels or remakes yet
Best is suggestive. It’s a weird movie but I wish there was more of David Cronenberg’s eXistenZ. Maybe a sequel since the movie ended on that possibility. But it’s probably going to end up repetitive, if not recursive.
And its an idea that has been explored in different other movies and series anyway. So as much as I liked the style of that movie, upon reflection, maybe it should just stay where it was left.