Ok, these aren't really secret societies they are organizations or clubs, but I'm a huge fan of The Da Vinci Code and love anything remotely secret, suspect, or questionable when it comes to organizations.
Charles Hansen, a regular contributor to the GHLL, has a few interesting newsletters on various societies. The June 1, 2010 newsletter features the Order of the Eastern Star. I became interested in learning more about this group when I was photographing ancestor's tombstones and found an imagine on the stone that I was unfamiliar with. You can see a photo of the stone, with the Order of the Eastern Star symbol here. Learning about the organizations our ancestors were involved in helps to give us more understanding of their life and fill in the pieces of our family history.