Welcome to the Bujinkan Hickey Dojo!
This is just a short list to get you started. I would recommend starting with Hatsumi Sensei's books.
Hatsumi Sensei's Books
In addition any other books by Dr. Masaaki Hatsumi
Other Books.
Arnaud Cousergue has just released a new book on Kihon Happô for Beginners. A very interesting tool for beginners and advanced students. Included with the book is a CD including some of the information in the book, the pictures, a flash file, and a a 20 minute film showing the movements in action with comments. 190 pages - 70 pictures.
Exploring the essence of the Martial Arts. By Alex Esteve
Also non Bujinkan related :-
More Sites with good reading lists: