The Ancient Middle and South Americans. Though the Spanish found a number of long-depraved societies, their ancient forebears (through more recent analysis) have shown indications of much deeper thought. These indicators include the use of a calendar and eras of time that bear comparison with the Hindu yugas.
The Pythagoreans - who may well have had links with the Hindus (Brahmins) and Celts, and studied Ancient Egyptian sciences.
The Kabbalah - A Judaic creation, and concerned with a pattern by which man may grow spiritually by action on himself. In some ways akin to the sciences of Buddhism, in my opinion.
About Theosophy and Helena Blavatsky.
The Gurdjieff International Review — a source of informed essays and commentary on the history, writings, and teachings of George Ivanovitch Gurdjieff. These pages include details about P.D. Ouspensky.
Jonathan Cainer is a leading British astrologer whose site gives mystical insight into this topic and a plethora of related issues written by him and esteemed colleagues. Click here for his page.