• The Phoenix Project
• Inside Cyber Warfare (O’Reilly)
• The Book of pf (No Starch Press)
• Absolute OpenBSD (No Starch Press)
• Modern X86 Assembly (Apress)
• How to Think Like a Computer Scientist Learning with Python (GreenTea Press)
• Art of the Start (Guy Kawasaki)
• Hacking Exposed Web Applications (McGraw Hill)
• Think Like a Programmer (No Starch Press)
• Code Craft (No Starch Press)
• Write Great Code II - Thinking Low Level, Writing High Level (No Starch Press)
• SDL Game Development (Packtpub)
• Mastering Nginx (Packtpub)
• Nginx HTTP Server (Packtpub)
• OpenVPN 2 Cookbook (Packtpub)
• Clean Code - A Handbook of Agile Software Craftsmanship (Pearson)
• Expert C Programming (Prentice Hall)
• Unix Essentials Featuring the Solaris 10 Operating System (Sun)
• The Linux Programming Interface A Linux And UNIX System Programming Handbook (No Starch Press)
• Operating System Concepts (Wiley)

Note on K&R C book: To be honest, I can not really recommend that to anyone unless s/he is a true geek and interested in history and how things were used to work back in the old days. (void main? seriously?)