Presentation Mode is a free AppleScript to wrap the UNIX "pmset" command and provide a convenient toggle between Presentation and Normal settings.
If we`re giving a presentation (on power or on battery), this script sets the display and the machine to never go to sleep, but allows the disk to shut down after 10 minutes of activity and run the internal screen at a lower brightness level when we`re on battery.
If we`re in normal mode and running on battery, this script sets the display to run at a lower brightness and to shut itself off after 1 minute of inactivity. The disk is shut off after 2 minutes of inactivity, and the whole machine will go to sleep after 5 minutes of inactivity.
If we`re in normal mode and running off of power, the script sets the display to itself off after 15 minutes of inactivity, and the disk to shut off after 10 minutes of inactivity. The system will never put itself to sleep.
All of these settings/timings are adjustable fairly easily by modifying the script.
This script is most useful if you place it in the /Library/Scripts folder and use the /Applications/AppleScript/AppleScript Utility application to turn on the Script Menu in the menu bar.