[livius]

For a good read:

The Making of the New Spirituality
James A. Herrick, Intervarsity Press, 2003

It's an excellent history of individual movements (starting a couple of hundred years ago, even prior to toking up in the Age of Aquarius) and a quite unnerving analysis of their current state in general and their effect upon modern thought.

[TBP]

Another excellent book is Spirits in Rebellion.