Masculine and Feminine: The Natural Flow of Opposites in the Psyche by Gareth S. Hill
A book, written from a Jungian perspective, that gives insight into how the masculine and feminine exists in all people, not only men or women. It explains how the masculine and feminine play a part in all our lives. Information about the book can be found here https://www.goodreads.com/book/show/226926.Masculine_and_Feminine.
Sentence completion assessments for ego development, meaning-making, and wisdom maturity, including STAGES
An extensive article with some interesting background information on sentence completion based methods (such as the SCT used by Greuter), and a whole bunch of other information that cannot be captured in a single sentence. See here: http://integralleadershipreview.com/15642-sentence-completion-assessments-for-ego-development-meaning-making-and-wisdom-maturity-including-stages-overview-and-summary-this-article-began-as-a-series-of-short-white-papers-providing-various/ or for PDF version (which I found much later) which is nicer to read http://www.perspegrity.com/papers/STAGES%20background_Murray.pdf
The process of individuation is one of the greater gifts Carl Jung left the world, you can read about it here: https://scottjeffrey.com/individuation-process-jungian-psychology/ Beware that that there are some "ads" that try to sell you self improvement material, but the summary is otherwise sound.
Evolving consciousness in leaders: promoting late-stage conventional and post-conventional development by Nicola Caroline Vincent
Leadershipship Maturity Framework: Stage Descriptions
Higher stages of human development
Cook-Greuter: Construct Aware Stage and the Fool Archetype
Consciousness quotient: CQ-i
Some interesting questions that in my experience serve as a reality check where you stand. The questions themselves sometimes more valuable than the answers you give. http://www.consciousness-quotient.com/what-is-the-cqi/ and http://www.consciousness-quotient.com/test-cq/
Vertical leadership development
Some whitepapers on key ingredients to leadership development: https://www.ccl.org/wp-content/uploads/2015/04/VerticalLeadersPart1.pdf and https://www.ccl.org/wp-content/uploads/2015/04/verticalLeadersPart2.pdf
The psychology of the quiet ego
A book that is based on vertical development stage theory like the work of Greuter, but really focusing on the topic of leadership: https://www.researchgate.net/publication/23318406_Leadership_agility