Like a security program itself, learning about information security is always a process—never a finished state. Although we have learned the basics of networking; how to become a power user of Nmap (and the other tools in the Nmap suite); how to conduct a vulnerability scan; and, now, how to conduct a penetration test—there are millions of other topics available to pursue.

While there's no set curriculum to become a security professional or to continue one's education in the field, there are many more books on the subject—and many different topics to cover. I strongly recommend you to look into The Web Application Hacker's Handbook, if web application assessments is interesting to you. There are also countless books on Metasploit, Burp Suite Professional, exploit development, reverse engineering, malware analysis, and many more topics that you can explore.

Never stop learning!