Here are the tools I find indispensable as a sys admin:

- screen for accessing servers

- lshw for seeing Linux server hardware config

- cfengine for automating my system administration

- atop as an advanced top

http://www.atoptool.nl/downloadatop.php

atop uses color to show when a subsystem goes over warn/critical threshold. it can be run in present time, or can be used to go back in time and "play back the tape".