What are some of the best "solitary" films?

-No sequels/prequels/midquels/spin-offs
-No remakes/reboots (as films or TV shows... I don't wanna count things like video game tie-ins or novelizations... stage adaptations may be iffy but are probably fine)
-Not adapted from any other work of fiction or based on specific real-life events (ie, specific people; historical fiction is fine)

Just doing a very small amount of research, here are a few big ones I came up with:
Citizen Kane
Eternal Sunshine of the Spotless Mind
Good Will Hunting
Inception
Pulp Fiction
Spirited Away
The Sixth Sense
The Sting
Taxi Driver
The Truman Show