Through history there have been many secret societies and conspiracy theories about those societies. This is a list of 10 of the most famous and popular secret societies or alleged secret societies.
1. Skull and Bones [Wikipedia]
Members of the Skull and Bones (George Bush is left of the clock) 
The Order of Skull and Bones, a Yale University society, was originally known as the Brotherhood of Death. It is one of the oldest student secret societies in the United States. It was founded in 1832 and membership is open to anelite few. The society uses masonic inspired Secret Societies: Insi... Best Price: $2.10 Buy New $7.00 (as of 05:55 EST - Details) rituals to this day. Members meet every Thursday and Sunday of each week in a building they call the “Tomb”.
According to Judy Schiff, Chief Archivist at the Yale University Library, the names of the members were not kept secret until the 1970s, but the rituals always have been. Both of the Bush presidents were members of the society while studying at Yale, and a number of other members have gone on to great fame and fortune.
The society is surrounded by conspiracy theories; the most popular of which is probably the idea that the CIA was built on members from the group. The CIA released a statement in 2007 (coinciding with the popularity of the film The Good Shepherd) in which it denied that the group was an incubator for the CIA. You can read that document here.
2. Freemasons [Wikipedia]
Freemasons Annual Meeting 
The Grand Masonic Lodge was created in 1717 when four small groups of lodges joined together. Membership levels were initially first and second degree, but in the 1750s this was expanded to create the third degree which caused a split in the group. When a person reaches the third degree, they are called a Master Mason.
Masons conduct their regular meetings in a ritualized style. This includes many references to architectural symbols such as the compass and square. They refer to God as “The Great Architect of the Universe”. The three degrees of Masonry are: 1: Entered Apprentice, this makes you a basic member of the group. 2: Fellow Craft, this is an intermediate degree in which you are meant to develop further knowledge of The True Story of the ... Best Price: $2.62 Buy New $15.00 (as of 01:20 EST - Details) Masonry. 3: Master Mason, this degree is necessary for participating in most masonic activities. Some rites (such as the Scottish rite) list up to 33 degrees of membership.
Masons use signs and handshakes to gain admission to their meetings, as well as to identify themselves to other people who may be Masons. The signs and handshakes often differ from one jurisdiction to another and are often changed or updated. This protects the group from people finding out how to gain admission under false pretenses. Masons also wear stylized clothing based upon the clothing worn by stone masons from the middle ages. The most well known of these is the apron.
In order to become a Mason, you must generally be recommended by a current mason. In some cases you must be recommended three times before you can join. You have to be at least 18 years old and of sound mind. Many religions frown upon membership of the Masons, and the Roman Catholic Church forbids Catholics to join under pain of excommunication.
3. Rosicrucians [Wikipedia]
Secret Symbols of the Rosicrucians
The Rosicrucian order is generally believed to have been the idea of a group of German protestants in the 1600s when a series of three documents were published: Fama Fraternitatis Rosae Crucis, Confessio Fraternitatis, and The Chymical Wedding of Christian Rosenkreutz anno 1459. The documents were so widely read and influential, that the historian Frances Yeats refers to the 17th century as the Rosicrucian Enlightenment. The first document tells the story of a mysterious alchemist (Christian Rosenkreuz) who travelled to various parts of the The Illuminati: Facts ... Best Price: $1.77 Buy New $13.85 (as of 12:55 EST - Details) world gathering secret knowledge. The second document tells of a secret brotherhood of alchemists who were preparing to change the political and intellectual face of Europe. The third document describes the invitation of Christian Rosenkreuz to attend and assist at the “Chemical” wedding of a King and Queen in a castle of Miracles.
Current members of the Rosicrucian Order claim that its origins are far more ancient than these documents. The authors of the documents seemed to strongly favor Lutheranism and include condemnations of the Catholic Church. Rosicrucianism probably had an influence on Masonry and, in fact, the 18th degree of Scottish Rite Masonry is called the Knight of the Rose Croix (red cross).
There are a large number of Rosicrucian groups today – each claiming to be closely tied to the original. Of the two main divisions, one is a mix of Christianity with Rosicrucian principles, and the other is semi-Masonic. The Masonic type tend to also have degrees of membership.