Re: If you could buy just ONE book about Aikido techniques, what would it be?
"Kodo: Ancient Ways" by the late Rev. Kensho Furuya Sensei. It's not about Aikido techniques so much as it is about Aikido approach and philosophy. He also has an excellent series of videos called "The Art of Aikido", which are great for kihon waza, Aikido history and dojo etiquette. "Aikido and the Dynamic Sphere" by Oscar Ratti is a classic for both its technical content and illustrations. "Aikido and the Harmony of Nature" by Mitsugi Saotome is also a nice reference. Books are great tools, or rather good books are great tools. After all, Osensei and virtually every other prominent teacher of Aikido have written on the matter at some point, or another albeit with varying degrees of success.