Eric Ligman a Microsoft Employee does a yearly round up of free books regarding Microsoft products. On July 11th he posted this years list. They range in categories from Azure to System Center. I found the best way to grab them all is using the Firefox plugin DownloadThemAll. The feature to grab all .pdf files from the article was able to save me some time in gathering all the documents.
Check it out here
Humble Bundle Cyber Security Book Bundle presented by Wiley
For only one dollar you can get four ebooks on Threat Modeling, Social Engineering, Reverse Engineering, and Hacking web applications.
The next tier is eight dollars and includes books written by Mitnick and Schneier. I've been meaning to review some of the Mitnick books here and Scheier is a highly respected member of the cyber security community. You can follow Scheier over at Scheier on Security
The final tier caps at fifteen dollars, and includes Five more books for a total of Fourteen eBooks on cyber security many of which are valued over fifteen dollars individually.
Support humble bundle and charities while picking up valuable security resources here.
Time is running out!