Western mysticism

One of the oldest forms of western mysticism is called Emanationism.

Emanationists such as Pythagoras, Plotinus, and others argued that complex patterns in nature were a natural consequence of procession from the One (Hen, Absolute).

According to Emanationism, the Absolute, its nature and its activity must be inseparably one thing only, namely will, such that the nature and activity of the Absolute is both one and the same (again, will) and by its very nature is also its activity ‘to will’ and wills things to be or occur, thereby maintaining the center of the logical system of Emanationism. In addition, agnosis, or the lack of Subjective gnosis, is a primordial privation which must be corrected before a metaphysical "Oneing" (Plotinus) can occur. Through this process, the transcendent yet immanent will of individuals is made self-reflexive by recollecting back further and further. Eventually it will reach that nature, the Noetic (and real) self, which is antecedent to the phenomenal, corporeal self. The ontologically transcendent yet immanent Self is seen as being one's unactualized nature, and this nature will remain unactualized until contemplation is brought to fruition, thereby bringing into actuality what had been merely potential.

According to this paradigm, creation proceeds as an effulgence from the First Principle (the Absolute or Godhead). The Supreme Light or Consciousness descends through a series of stages, gradations, worlds or hypostases, becoming progressively more material and embodied. In time it will turn around to return to the One (epistrophe), retracing its steps through spiritual knowledge and contemplation.

(above is from Wikipedia)
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Update (Aug 31, 2009):

In reply to a question I sent to Talat Halman (Assistant Professor of Religion, Central Michigan University) about the relation between Neo-Platonism and Sufism, and the nature of Islamic Illuminationist philosophy, he sent me the following reply:

"The reason Illuminationism (ishraqiyya) figures in is that it's a Persian Sufi stream (attributed to Yahya Suhrawardi d. 1191) that focuses on an ontology of light verses dark. When I saw the intro to the long-lost Meher Baba book Infinite Intelligence, I recognized this stream. The two major fiigures to follow up on are Yahya Suhrawardi and Mulla Sadra.

"Sufism is an ocean fed by many streams, a set of (sometimes almost) vaguely interrelated phenomena that would best be called spirituality rather than mysticism. Neo-Platonic terminology is used by many Sufis (just as alchemical metaphors are) but this does not exactly make them neo-Platonists. So there are many Sufis who have used the concepts. Especially prominent among them are the Ishraqiyya (Illuminationists) who include in their lineage Hermes, Zarathustra, Plato, Empedecles, and I think Plotinus."

~Talat Halman