Every system administrator should hone their public speaking skills for those times when you have to present your projects to the higher ups or train the staff on the new software.
Today, there are a variety of excellent sources of how to improve your public speaking – several from Guy Kawasaki. Guy has some tips that he received from his buddy Doug Lawrence. One he titled “Speaking as a Performing Art“, and a week later “Bite Your Tongue: Eight More Ways to Improve Your Presentations“.
Some tips that stood out to me (not in any particular order) are:
Don’t overwhelm the audience. Be entertaining but use moments of silence, soft speech, and slow cadence.
Skip the tea. Tea is an astringent and will close your voice down.
Use your eyes all the time. Hand gestures, pacing around the platform can all be useful tools in presentation, but the eyes…ah, the eyes have it!
Move away from center to make your point. When you come to a place in your presentation where you really want people’s attention, move to the left or right of your primary speaking position.
If those 15+8 tips from Guy Kawasaki weren’t enough, from Ian’s Messy Desk, Ian McKenzie has 10 ways to improve your public speaking.
As always, the ultimate place to practice public speaking is with your local Toastmasters organization. Why not join today?
UNIX Administratosphere 
Thanks for the link, David. The years spent at Toastmasters is some of the best investment of time I’ve made.