gistfile1.txt

ViM
Emacs
Terminal multiplexers (screen / tmux)
iptables (filtering, NAT, etc), or other packet filters
Dealing with security incidents (forensics, reactions, etc)
Anything to do with Windows *at all*.
How TCP and UDP work
Setting up a web server (apache probably) and how HTTP works
Setting up a mail server and how SMTP works
Setting up LDAP for centralised auth
Data center management (power, inventory, cabling, etc)
Setting up and managing a VM cluster (vmware? kemu? xen? whatever people have experience in)
Setting up and managing centralised logging with syslog, maybe add on logstash
Setting up and managing Chef, Puppet, at a medium scale (100 - 1000 hosts)
Anything on soft-skills (time management, communication, project management, interacting with other teams, etc)