Flavorwire has a great list of their 50 scariest short stories, many of which are available to read online. The list includes a lot of obvious, undeniable classics by authors like Ray Bradbury, Richard Matheson, H.P. Lovecraft, Edgar Allan Poe, and M.R. James, as well as some contemporary favorites, like Joyce Carol Oates, Kelly Link, and Mary Gaitskill.
I strongly endorse all the ones I’ve read from this list and I’m excited to check out those I haven’t read. Yay spooky stories!