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
True, it’s been talked about probably since District 9 came out, but in recent interviews he says there is a partial screenplay written but is just wrapped up in Oats Studios atm