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
Thankfully the Rock’s remake seems to have been scrapped (fingers crossed it stays that way), so Big Trouble in Little China (hence my name).
I’d also say The 'Burbs (one of my favorites) but it just got a series.