This one is a favorite of Lee Pavlik. Caffeine is a small application that sits in the notification area of your menu bar (by the clock) and all it does is keep your display on. This comes in handy when you’re giving presentations and want your computer constantly active.
After you install it, all you have to do is click the coffee cup icon and it’s activated (full cup)—your Mac won’t go to sleep, the screen won’t dim, and the screensaver won’t start. Click it again to deactivate (empty cup) and let your Mac sleep normally.
Download Caffeine now from Lighthead Software.