Our Macs work hard, and sometimes they get sleepy. But that doesn't mean they can slack off on the job! To keep your Mac alert and ready to go, check out Caffeine. It's a tiny little app (and at 48KB, we mean tiny!) that puts an icon in your menu bar. Give it a click to prevent your Mac from going to sleep, putting the disk to sleep or dimming the screen. Click again to remove these restrictions. It's quicker than launching system preferences and adjusting those settings manually, and convenient for those overnight downloads. Caffeine is universal and free.
Alternatively, try out Jiggler, which periodically "jiggles" your cursor to prevent your Mac from sleeping or launching a screensaver. Like Caffeine, Jiggle is universal and free. Now tell your Mac to get to work!