Common roadblocks to Linux adoption, Demystified

http://www.debiantutorials.org/content/view/181/264/

Interesting introductory links from the article:

• Linux Commands
• Basic Linux Commands
• Linux Tar command
• More Common Commands
• file Management Commands
• Basic Admin Commands, et al
• Way Useful

DebianWiki - LDAPAuthentication

http://wiki.debian.net/index.cgi?LDAPAuthentication

Newer documentation: http://wiki.debian.org/LDAP

Universal Command Guide for Operating Systems

http://www.allcommands.com/
http://www.allcommands.com/solaris%20commands%20list.html (broken link - much less useful right now)

Update
New website address: http://www.tomshardware.com/ucg/