To add to the constants list: rsync, some sort of firewall (iptables, apf-firewall, etc.), netstat, sed, awk, logrotate, lsof.

Hanging out with other sysadmins is better than a book. I find that information in books becomes outdated pretty quickly. Try new stuff in a development environment, and then pray they work the same when you go to production (often they won't - so follow the golden rule - back up everything).