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
12 angry men was remade
A remake isn’t a sequel
Not sure if it was possibly edited, but OP did specify sequel or remake
Good point, though the person you’re responding to only said it didn’t have a sequel.