Additional Resources:

The Enneagram Institute -- Don Richard Riso & Russ Hudson, two foremost authorities on enneagram offer a wealth of information on the types, the interaction between the types, and recommendation for personal growth. There is an online test for newbies as well as in-depth information for enneagram experts.

The Wisdom of the Enneagram
The Complete Guide to Psychological and Spiritual Growth for the Nine Personality Types. A book we highly recommend to further explore the enneagram.