Well, since Dr. Yang is my grandmaster in southern white crane an Yang tai chi, I would recommend alot of his books, especially discussions on fa jing, candle punching, and different forms of qi gong. Also, the I ching (book of change), Yang Tai Chi Classics by Yang Cheng Fu, the Art of War by Sun Tzu (still the best book going on fighting strategy), the Book of Five Rings by Musashi (I know, I am all kung fu/tai chi, but reading the approach to the sword and fighting by the greatest Japanese swordsman, and especially his 21 ways of going at it alone, are priceless), Kung Fu Elements by Liang Shou Yu (Dr. Yang and Jeff Bolt love him!), Teachings of Buddha (from a peaceful and relaxation aspect, can do nothing but help one's internal practice), Ying Jow Pai Eagle claw (the second book with the first 26 locks) by Leung Shum as well as his book on Wu style tai chi (I never learned Wu from him, only Yang from Jeff and Dr. Yang), and the History of Chinese Martial Arts. These are ones I would start off with, and yes in a few cases I am biased toward my teachers' books....LOL!! Maybe for publicizing, I can get another lesson in having my butt kicked, or learning how to relax when they tell me to relax, which after all of these years only makes me tense!!!
