I think good books are the most important thing to put in your own professional toolbox.
All the books listed here are my own books, often buyed after suggestions by someone in the online community. Unfortunately part of the books listed here are a bit outdated.

Unix books for power users

	Unix Power Tools by Jerry Peek, Tim O’Reilly and Mike Loukides – O’Reilly and Associates 1993 A very good book where a user can learn how to become a truly power user; you can find here anything from organizing your directory, to using shell scripts, find, awk and tons of others interesting things. A Must Have for any serious unix user.
	X User Tools by Linda Mui and Valeria Quercia – O’Reilly and Associates 1994 A good book about the X-Window system with many tips and suggestions to be more productive and to have more fun, but not so useful as Unix Power Tools

Unix System Administration

	Unix System Administration Handbook by Evi Nemeth, Garth Snyder, Scott Seebass – Perentice Hall 1989 A very good book, particularly useful for newbies to Unix System Administration, but very useful also to more experienced people. A Must Have
	Practical Unix Security by Simons Garfinke and Gene Spafford – O’Reilly and Associates 1994 Very interesting book about unix security, its vulnerability and practical countermeasures. A Must Have for everyone working in a security hostile environment.
	TCL and the TK toolkit by Jhon K. Ousterhout – Addison Wesley 1994 The official guide to the preferred scripting language for the X-Window system. A Must Have if you wish to give yourself and your users nice XWindows-aware utilities. I used Tcl/Tk in the past, before Perl 5 ant its Tk module, now I prefer to use Perl with its Tk module.

Solaris Administration

	Sun Performance and Tuning: Sparc & Solaris by Adrian Cockcroft – SunSoft Press Prentice Hall 1995 Probably a bit outdated today, but it has been very useful to me in the past. This comprehensive exploration of Sun performance and tuning contains the kind of hard recommendations and opinions that are often needed, but which are not normally found in the formal documentation.
	Automating Solaris Installations by Paul Anthony Kasper and Alan L. McClellan – SunSoft Press Prentice Hall 1995 It describes how to set up “hands-off” Solaris installations for hundreds of SPARC or x86 systems. It explains in detail how to configure your site so that when you install the Solaris environment, you simply boot a system and walk away; the software installs automatically!

Windows NT Administration

I don’t like this very bad designed, rudimentary Operating System, but I still need to administer some of this boxes.

Essential Windows Nt System Administration by Aeleen Frisch – O’Reilly and Associates 1998 Essential Windows NT System Administration helps you manage Windows NT systems as productively as possible, making the task as pleasant and satisfying as can be. It combines practical experience with technical expertise, helping you to work smarter and more efficiently. It also pays particular attention to developing your own tools by writing scripts in Perl and other languages to automate common tasks.

Perl Books

	Learning Perl by Randall Schwartz – O’Reilly and Associates 1993 A good introduction to learn Perl in short time. I still have the old 1993 edition covering Perl 4.
	Prgramming Perl by Larry Wall and Randall Schwartz – O’Reilly and Associates 1996 The reference guide to perl. A Must Have: you can’t say to be a Unix System Administrator without beeing proficient in Perl and you can’t setup a WWW server without writing cgi perl scripts. I have 3 copies of this book: one is alway on my desk at work, the other is near may PC at home and the other is the old 1991 edition covering Perl 4.
	Perl Cookbook by Tom Christiansen and Nathan Torkington – O’Reilly and Associates 1998 This collection of problems, solutions and examples for anyone programming in Perl covers everything from beiginner questions to advanced techniques. It contains hundreds of Perl recipes. This book is almost always on my desk; higly recommended.
	Advanced Perl Programming by Sriram Srinivasan – O’Reilly and Associates 1997This book covers complex techniques for managing production-ready Perl programs and explains methods for manipulating data and objects that may have looked like magic before. It also gives you the background you need for dealing with networks, databases and GUIs. Higly recommended.
	Win32 Perl Programming: The Standard Extensions by Dave Roth – Macmillan Technical Publishing 1999 In this excellent volume, author Dave Roth (who, coincidentally, is a prolific Win32 Perl module writer) thoroughly documents and explains the standard extensions for the Windows World. From ODBC to user authentication over networks and even playing .wav files, there’s something here to interest anyone using Perl on a Windows-based platform. Very useful to try to administer Windows NT systems the Unix way (without repeating the same hundreds of clickings on hundreds of different PCs, but executing simple scripts automatically on hundreds of different PCs).

Network Administration

	Lan Wiring: An Illustrated Guide to Network Cabling by James Trulove – McGraw-Hill 1997 You can’t administer a LAN without understanding the Physical Layer; for this reason this is an invaluable book. Cabling determines not just how effectively a network design can be implemented, but also its performance and longevity. This how-to guide provides complete details about methods, practices, and standards for installing and maintaining effective local area network wiring. Popular cabling topolgies such as Ethernet, Token Ring, Arcnet, FDDI, and ATM are fully covered.
	TCP/IP Network Administration by Craig Hung – O’Reilly and Associates 1992 Essential book for anyone adminstering a TCP/IP network, full of practical advice and suggestions. A Must Have
	Managing NFS and NIS by Hal Stern – O’Reilly and Associates 1992 Nice book with good advice and practical suggestions. Higly recommended to Unix LAN administrators.
	DNS and BIND by Paul Albitz & Cricket Liu – O’Reilly and Associates 1992 Contains all you need to know about the Internet’s Domain Name System (DNS) and the Berkeley Internet Name Domain (BIND), its UNIX implementation. It’ absolutely necessary to confiugure named without problems
	Sendmail by Bryan Costales, Eric Allman, Neil Ricket – O’Reilly and Associates 1993 Essential book to successful setup sendmail at your site. I ask myself how sendmail was setted up before this book. The only drawback is that Sendmail+IDA is not explained in full detail. A Must Have for every Mail Administrator.
	Managing UUCP and Usenet by Tim O’Reilly and Grace Todino – O’Reilly and Associates 1992It was an essential book when Internet was mainly a uucp network to exchange usenet news using the C-news system. Today with everyone having a direct internet connection and with INND as the preferred news system there is no much need for this kind of book.
	Managing Internet Information Services by Cricket Liu, Jerry Peck, Russ Jone, Bryan Buus and Adrian Nye – O’Reilly and Associates 1994 An overview of setting up telnet, ftp, gopher, wais, www and others internet services, everything you find in this book you can find on line but with more difficulties.
	Firewalls and Internet Security by William R. Cheswick Steven M. Bellovin – Addison-Wesley 1994 A Must Have for anyone responsible for setting up an Internet firewall. This book is full of practical advice based on first hand experience in repelling hackers at AT&T.

WAN Administration

	How to Manage Your Network using SNMP by Marshall T. Rose and Keith McCloghrie – Prentice Hall 1995 A good introduction to Simple Network Management Protocol and to network management using this protocol.
	Managing Ip Networks With Cisco Routers by Scott M. Ballew, Michael Loukides – O’Reilly & Associates 1997 A very very good book about routing and routing protocols. It discusses issues like how to select routing protocols and how to configure protocols to handle most common situations. It also discusses less esoteric but equally important issues like how to evaluate network equipment and vendors and how to set up a help desk. Although the book focuses on Cisco routers, and gives examples using Cisco’s IOS, the principles discussed are common to all IP networks, regardless of the vendor you choose.
	Cisco Tcp/Ip Routing Professional Reference by Chris Lewis – McGraw Hill Text 1997 All the answers on how to use Cisco’s TCP/IP routers will be found in this comprehensive book which has all the hands-on information that Cisco’s manuals sorely lack. It provides complete coverage from protocol and implementation basics to security concerns, performance troubleshooting, and migrating to Cisco routers. Higly recommended.

Text Processing Books

	LaTeX a Document Preparation System by Leslie Lamport – Addison Wesley 1986 The Official Book about the preferred text processing system in the online community. A Must Have for who prefers a structural oriented approach in writing documentation instead of the more beatiful but less powerful WYSIWYG approach.>
	Making TeX works by Norman Walsh – O’Reilly and Associates 1994 Everything you find in this book you can find on the Internet, but it is very nice to have all the materials, fonts, utilities and LaTex related tools explained in one place.

Microsoft Windows Books

	Unauthorized Windows 95 by Andrew Schulman – McGraw-Hill 1994 A detailed Windows ’95 analysis to find that it’s not a new and true operating system, but a good DOS son.
	Programming Windows by Charles Petzold – Microsoft Press 1990 A classic book on Windows Programming. When C was the only language to use in writing Windows programs this book was on every Windows programmer’s desk.
	Microsoft Windows ’95 Resource Kit – Microsoft Press 1995 The Microsoft Official Guide for corporate PC Network Administrators. As often in the PC/Windows world this guide has more than 1.000 pages but has few real information very disorganized and with general concepts intermixed with bullet proof installation instructions. I don’t like this guide but probably it’s a necessity in the corporate environment.

Oracle Books

Oracle The Complete Reference by George Kock and Kevin Loney – Oracle Press 1995 A simple, clear, concise and complete guide to Oracle database and its SQL. Highly recommended