1. Aldous Huxley’s Brave New World. It’s a must read if you’re into dystopia. Unlike Orwell, Huxley doesn’t focus on politics of his time. Specially good to read alongside Island, an utopia of the same author, dealing with similar topics (society, drugs, the human condition).
2. Anthony Burgess’ A Clockwork Orange. It has some satirical vibes, but it is not a good book to read if you’re feeling down (content warning: sexual violence). It focuses on a teen gang leader in the near future, and talks about themes like the impact of free will on morality.
3. William Golding’ Lord of the Flies. Technically not a dystopia, but it “scratches” the same itch. It’s about a bunch of kids dumped in an island, without adult supervision, and the resulting nasty proto-society that they build from it.
4. Yevgeny Zamyatin’s We. It’s perhaps one of the grandparents of the genre; it talks about individuality on a society controlled by a state that managed to conquer the whole globe.

There’s also Ayn Rand’s Atlas Shrugged. I don’t recommend it - the book is basically a “if Orwell was right-wing, soapboxing instead of trying to explain what’s going on, and with poor writing skills”. Seriously.