After reading the Illuminati thread, I did a quick Wicki search and found several "secret" groups:
http://en.wikipedia.org/wiki/Freemasonry
“Freemasonry is a fraternal organisation that arose from obscure origins in the late 16th to early 17th century. Freemasonry now exists in various forms all over the world, with a membership estimated at around five million, including just under two million in the United States and around 480,000 in England, Scotland and Ireland.[1][2] The various forms all share moral and metaphysical ideals, which include, in most cases, a constitutional declaration of belief in a Supreme Being.[3]
The fraternity is administratively organised into Grand Lodges or sometimes Orients, each of which governs its own jurisdiction, which consists of subordinate (or constituent) Lodges. Grand Lodges recognise each other through a process of landmarks and regularity. There are also appendant bodies, which are organisations related to the main branch of Freemasonry, but with their own independent administration.
Freemasonry uses the metaphors of operative stonemasons' tools and implements, against the allegorical backdrop of the building of King Solomon's Temple, to convey what has been described by both Masons and critics as "a system of morality veiled in allegory and illustrated by symbols."[4][5]”
http://en.wikipedia.org/wiki/Theosophy
"Theosophy is a doctrine of religious philosophy and metaphysics. Theosophy holds that all religions are attempts by the "Spiritual Hierarchy" to help humanity in evolving to greater perfection, and that each religion therefore has a portion of the truth. The founding members, Helena Petrovna Blavatsky (1831–1891), Henry Steel Olcott (1832–1907), and William Quan Judge (1851–1896), established the Theosophical Society in 1875."
http://en.wikipedia.org/wiki/Rosicrucianism
"Rosicrucianism is the theology of a secret society of mystics, allegedly formed in late medieval Germany, holding a doctrine "built on esoteric truths of the ancient past", which, "concealed from the average man, provide insight into nature, the physical universe and the spiritual realm."[1] It is symbolized by the rosy cross.
Between 1607 and 1616, two anonymous manifestos were published, first in Germany and later throughout Europe.[2] These were Fama Fraternitatis RC (The Fame of the Brotherhood of RC) and Confessio Fraternitatis (The Confession of the Brotherhood of RC). The influence of these documents, presenting a "most laudable Order" of mystic-philosopher-doctors and promoting a "Universal Reformation of Mankind", gave rise to an enthusiasm called by its historian Dame Frances Yates the "Rosicrucian Enlightenment".[3]
Rosicrucianism was associated with Protestantism and in particular Lutheranism.[4] According to historian David Stevenson, it was also influential to Freemasonry as it was emerging in Scotland.[4] In later centuries, many esoteric societies have claimed to derive their doctrines, in whole or in part, from the original Rosicrucians. Several modern societies, which date the beginning of the Order to earlier centuries, have been formed for the study of Rosicrucianism and allied subjects."
http://en.wikipedia.org/wiki/Ordo_Templi_Orientis
"Ordo Templi Orientis (O.T.O.) (Order of the Temple of the East, or the Order of Oriental Templars) is an international fraternal and religious organization founded at the beginning of the 20th century. English author and occultist Aleister Crowley has become the most well known member of the order.
Originally it was intended to be modelled after and associated with Freemasonry,[1] but under the leadership of Aleister Crowley, O.T.O. was reorganized around the Law of Thelema as its central religious principle. This Law—expressed as “Do what thou wilt shall be the whole of the Law" [2] and "Love is the law, love under will” [3]—was promulgated in 1904 with the dictation of The Book of the Law.
Similar to many secret societies, O.T.O. membership is based on an initiatory system with a series of degree ceremonies that use ritual drama to establish fraternal bonds and impart spiritual and philosophical teachings.
O.T.O. also includes the Ecclesia Gnostica Catholica (EGC) or Gnostic Catholic Church, which is the ecclesiastical arm of the Order. Its central rite, which is public, is called Liber XV, or the Gnostic Mass."
http://en.wikipedia.org/wiki/Thule_Society
"The Thule Society (German: Thule-Gesellschaft), originally the Studiengruppe für germanisches Altertum ("Study Group for Germanic Antiquity"), was a German occultist and völkisch group in Munich, named after a mythical northern country from Greek legend. The Society is notable chiefly as the organization that sponsored the Deutsche Arbeiterpartei (DAP), which was later transformed by Adolf Hitler into the National Socialist German Workers' Party (Nazi Party). However, there is no evidence that Hitler ever attended the Thule Society.[1]"
http://en.wikipedia.org/wiki/Illuminati
"Illuminati (plural of Latin illuminatus, "enlightened") is a name that refers to several groups, both historical and modern, and both real and fictitious. Historically, it refers specifically to the Bavarian Illuminati, an Enlightenment-era secret society founded on May 1, 1776. In modern times it is also used to refer to a purported conspiratorial organization which acts as a shadowy "power behind the throne", allegedly controlling world affairs through present day governments and corporations, usually as a modern incarnation or continuation of the Bavarian Illuminati. In this context, Illuminati is often used in reference to a New World Order (NWO). Many conspiracy theorists believe the Illuminati are the masterminds behind events that will lead to the establishment of such a New World Order."
http://en.wikipedia.org/wiki/Bilderberg_Group
"The Bilderberg Group, Bilderberg conference, or Bilderberg Club is an annual, unofficial, invitation-only conference of around 130 guests, most of whom are persons of influence in the fields of politics, banking, business, the military, and media. Each conference is held under intense security and secrecy.
The original conference was held at the Hotel de Bilderberg, near Arnhem in The Netherlands, from 29 May to 31 May 1954. It was initiated by several people, including Józef Retinger, concerned about the growth of anti-Americanism in Western Europe, who proposed an international conference at which leaders from European countries and the United States would be brought together with the aim of promoting atlanticism – better understanding between the cultures of the United States and Western Europe in order to foster cooperation on political, economic, and defense issues.[1] Retinger approached Prince Bernhard of the Netherlands, who agreed to promote the idea, together with Belgian Prime Minister Paul Van Zeeland, and the head of Unilever at that time, Dutchman Paul Rijkens. Bernhard in turn contacted Walter Bedell Smith, then head of the CIA, who asked Eisenhower adviser Charles Douglas Jackson to deal with the suggestion.[2] The guest list was to be drawn up by inviting two attendees from each nation, one of each to represent conservative and liberal points of view.[1] Fifty delegates from 11 countries in Western Europe attended the first conference along with 11 Americans.[3]
The success of the meeting led the organizers to arrange an annual conference. A permanent Steering Committee was established, with Retinger appointed as permanent secretary. As well as organizing the conference, the steering committee also maintained a register of attendee names and contact details, with the aim of creating an informal network of individuals who could call upon one another in a private capacity. Conferences were held in France, Germany, and Denmark over the following three years. In 1957, the first US conference was held in St. Simons, Georgia, with $30,000 from the Ford Foundation. The foundation supplied further funding for the 1959 and 1963 conferences.[2]"