My subconscious mind must believe there exists, deep in the result set of an Amazon search, the one definitive book that will answer all questions about all things networking. Why else would I keep adding books to an already-crowded shelf? I'm still looking for the perfect reference, but in my quest I have collected a set of tomes that I keep turning to. Here are four you may find useful.
Unix System Administration Guide by Reiss and Rodin. This book is nearly 20 years old. Why bother with a dusty reference from a bygone age? The answer is the prevalence of Linux in networking appliances. In general, being able to find your way around Unix means you can find your way around Linux. And if you can find your way around Linux, you can run the networking appliances that have found their way into your data center. Though this book is useful to me, I admit it's time to update to a more current edition. The larger point remains that a network engineer without Unix and Linux knowledge isn't as effective as he or she could be.
TCP/IP, Second Edition by Feit goes back to 1996. "Ha--another ancient volume!" you scoff. Scoff not, skeptic. This outstanding reference book covers TCP/IP in the sort of depth you don't often get in the more topical books released by networking vendors. There's even some coverage of IPv6--yes, back in 1996. The book is loaded with tables and diagrams that support easy-to-understand text. Read it for yourself, and you'll learn nuances of TCP/IP that will help you overcome the challenges you run into on the job. Read it to your toddlers before bed and they'll be networking consultants before junior high (or, at least, very well rested).
Hacking Exposed: Web Applications, Second Edition by Scambray, Shema and Sima was released in 2006. A third edition was released in late 2010; that's the one you want should this topic interest you. And it should definitely interest you. Web applications, specifically HTTP transport and frequently paired applications such as SQL, are the most common way to deliver content to the people who need it. The more you understand about how Web applications work and how they are attacked, the better you'll be at troubleshooting them and securing them from the bad guys.
Perhaps you expected my book lists to contain only networking protocol guides. While I've had a few of those references over the years (and recommend the CCIE Routing & Switching Certification Guide by Odom, Healy, and Donohue for everyone in IT, not just CCIE candidates), I have been enriched as a network engineer by reading books that help me think of information technology as an integrated system, of which the network is only one part. Yes, you made it so that point A can talk to point B. But how well? The more you know about how applications communicate across the network, the better you'll be at making sure they have a pleasant conversation.
The books above are ink on paper. What about e-books? I do read e-books with a Kindle Fire or occasionally a laptop, but most of the technical documentation I read is PDFs of whitepapers, vendor reference documentation, and product data sheets. That sort of information is quickly obsolete, and is easily stored (and disposed of) in e-book form. For references with greater shelf-life, I still favor paper books.
Ethan Banks is CCIE #20655 and a 16+ year IT veteran. He has designed, implemented, and supported networks for government, banking institutions, higher education, and various corporations. He is a host of the Packet Pushers podcast and an independent blogger covering the data networking industry.