That would be O'Reilly, Addison/Wesley, Prentice Hall, and Morgan Kaufman, in about that order, for technical books. I've been disappointed, but very infrequently.
I avoid any of the TITLES THAT SHOUT!!!: "...for Dummies", "...for Idiots", "...UNLEASHED!", "...in 24 hours", etc. I find most contain largely superfluous fluff, waste shelf space (no mean consideration), insult my intelligence, and top out far too early. I've been surprised, but very infrequently.
A well written technical reference is both accessible to the novice and useful to the master. The SHOUTING books have missed this fact.
Essential books for Linux/Unix: Linux in a Nutshell, UNIX Power Tools, Nemeth, Snyder, Seebass, & Hein's UNIX System Administration Handbook. Beyond that, your purchases should be driven by your interests. My interests are broad <g>. Networking, security, crypto, general programming, project management, analysis and statistics, publishing tools...
Though my interests rarely lean toward Microsoft products, I've found Steve McConnell's Code Complete to be among the classics. While Microsoft's documentation series structure is a reasonably good one ("Using", "Running", "Resource Kit"), the content bogs in my experience. 'Course few others do better, though I've got the NT nutshell book from O'Reilly.
Classics are often well worth buying. Jon Bently's "Programming Perls" series, Kernigan and Pike's "The UNIX Programming Environment", and Kernigan and Ritchey's "The C Programming Language" are also near at hand. Not to mention Knuth and Stevens.
More important than books IMO is a good technical bookstore in which you can browse. Shout out to Stacey's in Palo Alto and San Francisco, Cody's in Berkeley, and as a fallback, Borders, which tends to do pretty well around the Bay Area and Chicago (two locales I'm familiar with). A local technical bookstore is a treasure. Let them know you appreciate them.
Karsten M. Self
SCO -- backgrounder on Caldera/SCO vs IBM
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