My Sister's Keeper: The novel concludes with Kate recovering from illness and Anna dying in a car accident, but the film ends with Kate dying from cancer and Anna winning an art scholarship to study in New York.
The Scarlet Letter: The novel concludes with Arthur Dimmesdale's death after revealing that he is the father of Hester's daughter, Pearl, but the 1995 film adaptation concludes with war breaking out between the Algonquins and the Puritans and Hester fleeing with Dimmesdale.
Jurassic Park: The novel ends with the dinosaur island being bombed, but the film concludes with the scientists and their team fleeing to safety on a helicopter.
The Notebook: The novel concludes with Allie, who is suffering from Alzheimer's, finally recognising Noah and the pair falling asleep together, but the 2004 film concludes with Noah and Allie dying in their sleep while clutching each other.
Watchmen: The graphic novel concludes with a giant squid creature attacking Manhattan, resulting in a new alliance between previously outlawed superheroes and the government, whereas the film adaptation concludes with Adrian Veidt launching an attack on New York using energy reactors and framing Doctor Manhattan.
Fight Club: The novel ends with the protagonist waking up in a hospital surrounded by Project Mayhem members after a botched suicide attempt, but the film closes with the narrator and Marla watching as Project Mayhem's plan to destroy the city plays out.
A Clockwork Orange: The novel concludes with Alex finding less joy in committing crimes and contemplating a regular life, however, the film concludes with Alex's therapy reversed and he still considers his violent urges.
Forrest Gump: The film's finale is significantly less gloomy, with Jenny and Forrest marrying and raising their kid after she succumbs to AIDS, but the novel ends with Forrest living on the street with his former commander and an ape named "Sue."
I Am Legend: The film's finale is a touch more positive, with Neville giving himself to safeguard both the cure for the sickness and two survivors, whereas the novel's ending has Neville peacefully resigned to death as the "infected" build a new civilization.
Lord of the Rings: The Return of the King: The novel concludes with the Hobbits returning to the Shire only to find it under siege, sparking a revolt, although the film's finale comes the "happily ever after" a little earlier and omits the Shire insurrection.