Admin.com: The companion site to Unix System Administration Handbook and Linux Administration Handbook.
Go Solo 2 - The Book: Authorized guide to version 2 of the single UNIX specification.
Linux Administration Made Easy: A published book made available online. Covers adding users to "Enterprise Computing."
Linux Quick Fix Notebook: Simple to use systems administration guide for setting up a Linux based website. Lots of practical examples and troubleshooting tips. This book was written specifically for busy systems administrators who need to quickly finish a project with just the essential background information for it all to make sense.
O'Reilly Linux/Unix Center: Features Linux and Unix books, resources, news and articles.