QuickSleep

QuickSleep offers an effortless way to put your Mac in sleep mode. QuickSleep allows you to turn off only your Mac's display, and nothing else within your computer — all hard drives, AirPort cards, and everything else stays on.

Yet, if you don't want to put your Mac in full sleep mode, you can simply lock your Mac or enable the screensaver so you can keep unwanted intruders out of your account.