I was listening to the KitchensinkWP podcast (episode E038) a few days ago when Adam Silver mentioned 2 WordPress eBooks were available at the Hot Off the Press WordPress dot com website. I checked the website and downloaded the 2 eBooks – Writing 101 and Writing 201.
While I was browsing through the website, I found three other eBooks available for download. You can see all 5 eBooks here: http://dailypost.wordpress.com/blogging-university-ebooks/
During my presentation at WordCamp Dayton on Find WordPress Help, I had made reference to the 30 plus eBooks that are available for free at the iThemes website. You can see the entire list of eBooks here: https://ithemes.com/publishing/