A Dweller on Two Planets by Phylos. This influential book was written in the 1890s and saw publication in 1905 six years after the death of the author (Frederick S. Oliver, who claimed he used automatic writing to channel the spirit of Phylos, a man from Atlantis whose body was in a temple on Mount Shasta, but whose spirit was on Venus). As out-there as that sounds to normal people (and that's not even a complete rendering of the situation), this book heavily influenced a great deal of what people believe about Atlantis these days. The views on Karma and Reincarnation have also been influential. As far as predictions, the author nailed television and atomic telescopes.
The text can be dense, but the descriptions of daily life in Atlantis from the social mores to the religion is fascinating. As far as New Age and Occult libraries are concerned, if you don't own a copy of this book, your library is incomplete.