Joe Nagata, arguably the "king" of NXT walker designers, has published a 193-page book of his creations. The book's page on Amazon's Japanese web site is here.
Joe also has several books available here. Could someone who reads Japanese confirm that this particular book of Joe's is available on yesasia.com? ("yesasia.com" doesn't provide cover images of Joe's books).
(This book on yesasia.com has the same number of pages and the same release date as the one listed on Amazon's Japanese site).
HOWEVER, someone who reads Japanese should confirm this.
If you're looking for Joe Nagata's introduction to making walking NXT robots, this is the one.
Koga has confirmed that the "yesasia.com" url mentioned in the first comment on this page is the correct one for buying Joe Nagata's book.
I've purchased from yesasia before and find them to be a reliable vendor. It generally takes a month to receive a book from them, if you live in the US.