I have heard about putting a monitor in "sleep... (by 3 users)

Sleep mode is suspend mode under another name, and it's activated inside the Power Profiles applet in the Control Panel. It's just a mode which lets the monitor turn off its main circuitry, save for the idle power circuit. When you press a key on the keyboard, or move the mouse, the monitor snaps out of suspend mode within a couple of seconds and you can continue to use it.
As well as altering the delay between idle time and your monitor going into Suspend mode, you can set how long your hard drives will stay active until they turn off (i.e. stop spinning after x hours idle)... It can be useful in a work situation. However, I don't bother with putting my monitor into suspend mode, as Windows sometimes messes up for me (it's a temperamental beast) and once the monitor's in Suspend mode, I can't get the damn thing back to normal mode which means I have to reboot. I just turn off the monitor at the switch on the front - it saves more power anyway, as even while the screen's in Suspend mode, it's still taking power from the mains (though only a small amount).
Another way to access the Power Profiles settings is via right-clicking on an empty bit of desktop real estate, going to Properties, then along to the Screen Saver tab and hitting the Power... button down the bottom of the window. You can access the same applet via the Control Panel directly if you're so inclined.