Linux Administration Made Easy - A published book made available online. Covers adding users to "Enterprise Computing." - http://tldp.org/LDP/lame/LAME/linux-admin-made-easy/
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 - http://www.quickfixnotebook.com/
Go Solo 2 - The Book - Authorized guide to version 2 of the single UNIX specification. - http://www.unix.org/gosolo2/
O'Reilly Linux/Unix Center - Features Linux and Unix books, resources, news and articles. - http://linux.oreilly.com/
Admin.com - The companion site to Unix System Administration Handbook and Linux Administration Handbook. - http://www.admin.com/