I'm surprised the no one has recommended not to buy any books. Between videos, articles, interviews, pictures, discussions, there is more information available online to anyone than ever before.
The content available via the internet is
the living book on aikido. You have the only book you need: a monitor to read from, and a keyboard input device. If you got here, you have "the" book.
If you've got a little money burning a hole in your pocket, go and buy a year's subscription to http://members.aikidojournal.com/ajm...ions-page.html