Learning and Mastering UNIX

The UNIX Reference Desk This contains virtually everything on UNIX, including various programs, text editors, applications, etc.
UNIX help for users
Chris Taylor's great hints on UNIX and VI
SCO UNIX Operating System Tutorial by Santa Cruz Corporation
UNIX FAQs - a superb site to clarify doubts
Unix Concepts at USC (very useful info on creating symbolic links and basics of t shell)
USAIL, a detailed and comprehensive UNIX tutorial
Unix Tutorial, by Scott Miller
A collection of documents for new and occasional users of Unix
The FTP server at Arizona State University has a collection of information and tips on using Unix .
A FAQ for UNIX programmers
My own, rather primitive, unix faq, based on questions to consultants/ info from friends This is under development.
Renaming multiple files instantly
Adding a line to all html pages (illustration of sed)

System Administration:

Unix System Administration by Frank G. Fiamingo
UNIX System Manager's Manual (SMM)
Administering SCO UNIX: A System Administration Guide by SCO
Unix Workstation Administration Tasks, by USAIL

UNIX Scripts and Programs