Aikido and the dynamic sphere did not appeal to me at all. Sure the drawings are nice but the information in the book is not that good (sometimes directly misleading).
I would suggest:
Effortless Combat Throws by Cartmell (not aikido but discuss proper throwing technique regardless of style with more explanations, details and clarity than all aikido books that I´ve read).
Total Aikido by Shioda (especially the first part regarding principles)
New Edition of Takemusu Aikido by Saito
Yurusu Budo by Nishio
If you aren't either doing Nishio aikido or you are already very experienced, I wouldn't recommend Yurusu Budo. A lot of what Nishio says is geared towards people who are already experienced, and it is quite different to many other styles. I got a lot out of this book, but only after training for 10 years and then training at a Nishio style dojo.