Quick Hide Windows by CronoSoft is great for hiding program windows with a press of a hotkey combination. You easily bring them back with another combo. Hiding the taskbar and desktop icons is just awesome. Password protection allows you to lock QHW to prevent intruders from trying to show invisible applications while you're gone. You can even lock your computer with QHW instead of a weak, easily hackable screensaver password.
) "Quick Hide Windows - Click to enlarge screenshot")