Re: If you could buy just ONE book about Aikido techniques, what would it be?
I have to agree with David that DVDs/videos are the best. There are a few problems with photos:
(1) Clarity, sometimes it's hard to see the hands or feet clearly
(2) Missing steps... sometimes you want to see exactly how the sensei went from A to B, and that's not possible with photos
(3) They don't capture the dynamism of movement... so it's hard to appreciate the flow in the technique
Of course, books are more convenient, less expensive and some books explain just that technique you are looking for/or in a style not found in DVDs... Books are also great for reading about people's thoughts on Aikido
Since you are just starting out in Aikikai style, I would recommend something that follows your school - otherwise, the terms and instruction can be confusing - e.g. you could be asking why they call the technique 'A', whereas you were taught it as 'B'... also the person in the photo/video does kotegaeshi (wrist turn) in one way from one attack, whereas you've been taught a different way from the same attack