Hahnemann Revisited, Luc De Schepper, MD (a very useful textbook for the serious student or practitioner on how to practice classical Hahnemannian homeopathy)
Principles of Homeopathic Philosophy, by Margaret Roy (Originally written as a textbook for those doing distance learning, this is an excellent course in homeopathic thinking!)
Hahnemann Revisited, Luc de Schepper, MD, PhD. (This is an excellent book on homeopathic methodology, with some emphasis on the use of LM potencies, Hahnemann's last major contribution to homeopathy.)
What About the Potency? A comprehensive guide to homeopathic potency and dosage by Michelle Shine, a British homeopath. (This book includes interviews with a dozen or so leading homeopaths and asks them how they determine the potency in a variety of situations. It is very instructive for showing the logic of different systems of prescribing.
For people interested in some of Dana Ullman's earliest writings, you can read his undergraduate thesis at U.C. Berkeley in 1975 on "Human Learning." Honor students at UC Berkeley who wish to have an independent major (and who do not want to have a regular generic major) are required to write a thesis. This paper on "Human Learning" provides insights into Dana's early synthetic and integrative thinking. The beginning of the article and its definition of "science" may be of special interest. Also, Dana creatively chose to use his own invented pronouns to replace the masculine emphasis of "he," "him," and "his," with "che," "chis," and "cher."