hi! :) i always recommend http://www.immortalgeisha.com/ it's the biggest website about geishas, but i think some parts of this site don't work recently -_- you can also click on photos i post, they usually lead to flickr pages with lots of information about currently working geishas.

Some okiyas have their own websites, like the one where Fukuho and Kofuku live: http://ochaya.kyo2.jp/

and also if you like Kyouka and Satsuki, you can read some cute facts about them here: http://koimaiko.com/cast/