Man, I've been down this rabbit hole a lot. For classic public domain stuff, Project Gutenberg is actually solid—they've got M.R. James, Sheridan Le Fanu, all those foundational writers. It's not flashy, but the writing does the work. For a more modern, curated feel, I sometimes poke around the horror sections of sites like ManyBooks or Standard Ebooks; they often have decently formatted collections. A lot of people swear by library apps like Libby, but availability really depends on your local library's catalog. Honestly, some of the most chilling stuff I've found lately has been in horror fiction podcasts that post their transcripts. It's not a traditional 'read,' but the storytelling is top-notch and completely free.
I'd be a little careful with sites that just aggregate user-submitted 'scary stories.' The quality is wildly inconsistent, and you'll wade through a lot of poorly written teenage angst to find one genuinely eerie tale. Sometimes the hunt is part of the fun, though.