Reddit reviews The Joyous Cosmology: Adventures in the Chemistry of Consciousness

Not really a guide but I love The Joyous Cosmology by Watts. Has a bit more woo than a materialist might like, but Watts' brand of woo is palatable and non-dogmatic -- more of a try "try THIS on for size" than a "so THIS is this the way the universe is."

You may also find The Secret Chief Revealed insightful in terms of the therapeutic benefits to tripping, and how to approach psychedelics seriously.

Prometheus Rising, while more of an owner's manual to the human mind than a tripping guide, can help with recognizing your own biases and trying new perspectives -- highly relevant to the psychedelic experience and beloved by many psychonauts.

It's from his book The Joyous Cosmology which is one of the better books about the psychedelic experience. There are some online versions but they are missing the photos (of abstract patterns from nature, mostly), so it is worth getting a physical copy.

"The Joyous Cosmology" is a wonderful exposé of Alan's experience using psychedelic drugs.

I also found "The Way of Zen" to be a really great explanation of the history of Zen as well as many Zen principles and ideas (through the lens of Alan's own philosophy, of course).

Alan Watts' autobiography is In My Own Way. However, it is within The Joyous Cosmology that he details his psychedelic experiences(s), if I recall correctly.

Aldous Huxley details his psychedelic experience(s) in The Doors of Perception.

Edit: Timothy Leary's autobiography is Flashbacks.