Attrition's Newbie Area - Newbie-oriented tutorials about stuff like UNIX and system penetration auditing.
Hackerthreads.org - Tutorials about networking, system administration and network utilities.
How to Become a Hacker - A short essay on becoming an old-guard hacker (NOT a cracker or phreaker).
Meta Description: [ How to become a REAL hacker. Not a cracker, saboteur, virus author, or other malicious bad guy, but the kind of hacker that built today's technologies. ]
Linux Documentation Project - Compilation of tutorials and HOWTOs for the linux operating system.
Meta Description: [ Command Prompt, Inc. is the largest and oldest US based commercial PostgreSQL support provider. We provide the only commercially viable integrated PostgreSQL replication solution, but also custom programming, and support. We authored the book Practical PostgreSQL, the procedural language plPHP, a... ]
The Happy Hacker - Home of the Guides to (Mostly) Harmless Hacking. Focus is mainly on Windows 95 and 98. Some mention of Windows NT.
Meta Description: [ Guides to (mostly) Harmless Hacking - GTMHH - Dedicated to good, old-fashioned harmless hacking ]
The New Hacker's Dictionary - Hacking jargon including information on writing style, hacker terms, and lamer-speak.
^Rob's WerLD - Contains information about viruses and trojans and their fixes. For newbies and advanced.
Dentistry Marketing for Newbies, Intermediate and Advanced Practitioners