I guess her most famous work, widely read in schools, is her short story "The Lottery."
I'm fond of her books, particularly The Haunting of Hill House and We Have Always Lived in the Castle.
THoHH is by far my favorite haunted house tale, but it's much more than that. It's a study of Eleanor, a young woman who's a bundle of neuroses. Eleanor has developed a daydreaming habit as a coping mechanism. Her inner world is quite rich:
“I could live there all alone, she thought, slowing the car to look down the winding garden path to the small blue front door with, perfectly, a white cat on the step. No one would ever find me there, either, behind all those roses, and just to make sure I would plant oleanders by the road. I will light a fire in the cool evenings and toast apples at my own hearth. I will raise white cats and sew white curtains for the windows and sometimes come out of my door to go to the store to buy cinnamon and tea and thread. People will come to me to have their fortunes told, and I will brew love potions for sad maidens; I will have a robin...”
Ultimately Eleanor's fanciful thinking takes her down a path of darkness
The other memorable character that Jackson created is Merricat Blackwood, the teenage narrator of WHALitC. Like Eleanor, she is extremely troubled. She's also an unreliable narrator. Jackson introduces us to her in grand fashion:
"My name is Mary Katherine Blackwood. I am eighteen years old, and I live with my sister Constance. I have often thought that with any luck at all I could have been born a werewolf, because the two middle fingers on both my hands are the same length, but I have had to be content with what I had. I dislike washing myself, and dogs, and noise. I like my sister Constance, and Richard Plantagenet, and Amanita phalloides, the deathcup mushroom… Everyone else in my family is dead."
If you haven't read any of Jackson's work since reading "The Lottery," check out her novels. You won't regret it.