You are aware right now, reading these words, and that awareness is the most familiar thing in your existence and simultaneously one of the least understood phenomena in the universe. Neuroscience can map which brain regions activate when you see the color red, but it cannot explain why there is something it is like to see red, why the neural correlates are accompanied by a subjective experience at all. Philosopher David Chalmers called this the "hard problem" of consciousness, and three decades later it remains genuinely unsolved. The easy problems, how the brain processes information, integrates sensory data, and generates behavior, are being picked off one by one. The hard problem has not budged. That gap between mechanism and experience is what makes this subject so compelling, and it is the territory these books map from radically different directions.
What connects these picks is range. Harris approaches consciousness as a neuroscientist who has spent decades meditating and argues that the feeling of being a self is a neurological artifact that dissolves under sustained attention. Huxley opened the doors of perception with mescaline in 1953 and wrote about what he found with a precision that still defines how we think about altered states. Nisargadatta Maharaj, a cigarette seller in Bombay, offers a contemplative investigation of awareness so rigorous it makes most academic philosophy look timid. Dennett provides the strongest materialist argument that consciousness is not what we think it is. Pollan takes the psychedelic question into clinical trials and comes back with something that neither the scientists nor the mystics fully predicted. These authors disagree with each other on fundamental points, and that disagreement is the point, because consciousness is a subject where intellectual honesty requires holding multiple frameworks at once.
If you are drawn to the scientific angle, start with Harris or Pollan. If you want the contemplative depth, I Am That and Be Here Now will take you further inside than any lab. If you like having your assumptions dismantled by careful argument, Dennett will oblige. The books here are best read in conversation with each other, because no single perspective can hold what consciousness actually is.