Sent to you by jdmumper via Google Reader:
No matter what type we are, we can observe the following about Inner Work: "We need to be willing to observe our resistance to reality, our attachment to our self-image, and our fear." (Understanding the Enneagram, 361)
Be aware of the transformational process, no matter what type you are. "It is necessary that we develop a whole, well-integrated personality before we can 'give it up' in the transformational process." (Understanding the Enneagram, 367)
"Once we understand 'not doing,' we see that the real struggle is to relax into greater awareness so that we can see the manifestations of our personality. By neither acting on our automatic impulses nor suppressing them, we begin to understand what is causing them to arise." (The Wisdom of the Enneagram, 346)
For more in "inner work" a good introduction for someone might be Inner Work: Using Your Dreams and Active Imagination for Personal Growth by Robert A. Johnson.
The Road Less Travelled & Beyond: Spiritual Growth in an Age of Anxiety by M. Scott Peck.
Again, introductions (though some less for a general reader, unless motivated to stick with themes etc that might be presently unfamiliar), but more from within the Christian tradition:
Heart of Flesh: A Feminist Spirituality for Men and Women by Joan D. Chittister
Care of Mind, Care of Heart: A Psychiatrist Explores Spiritual Direction by Gerald G. May.
Will & Spirit: A Contemplative Psychology by Gerald G. May.
The Awakened Heart: Opening Yourself to the Love You Need by Gerald G. May.
Addiction and Grace: Love and Spirituality in the Healing of Addictions by Gerald G. May.
As you'll be able to tell I have a very high regard for May (d. 2005) and his writing. May is the brother of Rollo May, and existential psychologist c.f. his writings of existential psychology collected in The Discovery of Being.
When the Heart Waits: Spiritual Direction for Life's Sacred Questions by Sue Monk Kidd.
A Hidden Wholeness: The Journey Toward and Undivided Life by Parker J. Palmer (see also the audio series An Undivided Life: Seeking Wholeness in Ourselves, Our Work & Our World).
Let Your Life Speak by Parker J. Palmer
Finally, from deeper within the Christian mystical tradition:
Mystical Theology: The Science of Love by William Johnston.
For more on the enneagram: The Enneagram: A Christian Perspective by Richard Rohr (and Andreas Ebert).
The Enneagram: Understanding Yourself and Others in Your Life by Helen Palmer.
The Essential Enneagram (revised and updated, 2009) by David Daniels and Virginia Price.
My Best Self: Using the Enneagram to Free the Soul by Kathleen Hurley and Theodore Dobson.