There are, as in many other religions of the world, several denominations of Wicca. These are derived from the eclectic idealism of the religion itself, and because of such, wicca is viewed in a way that suits the needs of the desires and beliefs of each practitioner. As stated previously, Wicca is comprised of a great deal of Dogma. Many will argue this statement blindly, because they're not well educated in the religion. Dogma exists because each practitioner has their own belief of who the Goddess and God are, and how worship to the Divine should be conducted. Their beliefs in how magick works also differs. This is dogma.
Alexandrian Wicca
This tradition was founded by Alex Sanders, in England. This is a tradition made with many Judeo-Christian and Ceremonial magickal elements. Covens work sky clad as a rule, and all eight sabbats are observed, as well as both the God and the Goddess being honored.
Eclectic Wicca
Many prefer to follow this tradition of Wicca. Not being a tradition to the word, the idea of being an Eclectic wiccan is that you borrow from many aspects of the Ancient Religions of the Earth. Some disrespect the Eclectic tradition because they view it as lawless. Remember, the only rule we must follow in Wicca is our rede of the Witches - 'An it harm None, Do as thou will.' Some prefer to follow the Gardnerian path, yet work robed. Others prefer to work with only four people, while others prefer to follow a Druid/Arch Mage path. All are valid, and acceptable. Those who do not accept the Eclectic view of Wicca have either fallen into a tradition comprised of much dogma, or they still have much to learn along their path in life.
Gardnerian Wicca
Founded by Gerald Gardner, this tradition was actually launched shortly after the second World War. Contrary to the belief of many, Aleister Crowley did NOT write the book of shadows for Gardner. Also, it was not Gardner who brought the rebirth of the Old Religion. This misconception has earned this tradition the mistaken idea that the Gardner Tradition is the only true trad in Wicca. The Goddess takes emphasis over the God in this tradition, with the female ranking above the male practitioner. Also, there is a 'system of degree' that does not allow for self-initiation into this tradition. There is also a rule where covens work sky clad, and they aim to have 'perfect couples' with equal numbers of males and females, paired, and the covens of Gardnerian are autonomous. Most who are members of this tradition claim it's the only true tradition. This is due to the misconception previously pointed out. However, fact remains that many still believe that it was Garnder that fathered Wicca.
Other Traditions
I've decided to mention the above because these are the only one's I've bothered to read up on, or I have no reference to others. I do have recommended reading that mentions much more, and that would be Raymond Buckland's Complete Book of Witchcraft. There is an excellent section that describes many traditions, and how they conduct themselves in ritual.
Books You Might Enjoy:
Confucius - Confucian Canon
Sepharial - Primary Directions Made Easy
Mike Nichols - Eight Sabbats Of Witchcraft
Michael Harrison - The Roots Of Witchcraft
Michael Bailey - Historical Dictionary Of Witchcraft
