Don briefly mentioned him but I would add only a few books to his excellent collection.
Yurusu Budo "The Budo of Acceptance". Shoji Nishio Shihan with Stan Pranin. Stan's book is the only one Shoji Nishio ever wrote, and gives the reader a great understanding of his philosphy and technique.
The Nishio Sensei Aikido Notebook 1&2 Lessons and Seminars of Shoji Nishio Shihan and complete Aiki-Toho-Iai.Sensei Steffi Varjan ( A 30 year student of Shoji Nishio Shihan it is very comprehensive and our unoffical training manual(s). )
Miyamoto Musashi. His Life and Writings. Kenji Tokitsu. Written by a lifelong Budoka; Tokitsu Shihan has made the study of Musashi his life's work, and should be read by anyone interested in the history of Japanese Budo.
Everyday Zen & Living Zen. Charlotte Joko Beck. Dharma Heir of Tazuin Mazumi Roshi; Joko Beck makes understanding Soto Zen very easy and helps us to live it in our daily lives... or as she used to put it... "Make Love Drive Freeway."