The Shining by Stephen King
When a struggling writer with a history of drug abuse and family issues takes his wife and kid to a haunted hotel to work as caretaker for the winter, stuff gets pretty crazy. Those familiar with the Stanley Kubrick movie will see a lot of similarities here, but Stephen King's novel is much more detailed and has practically an entirely different ending. Absolutely a must read for horror aficionados.
Scare Factor: 3 - Seeing Jack's downfall is definitely unsettling. The climax takes a long time to come but when it does, it is pretty darn intense.