Anyone know if there is a good biography of Takeda Sokaku out there?
Not precisely, perhaps, but there's
Edited by Stanley A. Pranin
The first book in English to explore the life of the enigmatic Sokaku Takeda with an authoritative essay by Aikido Journal Editor-in-chief Stanley Pranin.
Also contains interviews with Sokaku's top students including Tokimune Takeda, Yukiyoshi Sagawa, Chieko Horikawa, Yusuke Inoue, Takuma Hisa, Keisuke Sato, Katsuyuki Kondo, Hakaru Mori and Seigo Okamoto.
Also, the website itself has volumes of info. See "Sokaku Takeda Biography (1-9)" at http://aikidojournal.com/articles/article_index.asp
. Each URL is a teaser giving you a page of text with the offer to show the rest of the article if subscribe for a cheap (my opinion) $29.75 per year if you're not already a member.