I turn my monitor on and off a lot. The switch in the back is not very handy. I needed a software solution, so on my toolbar I added an icon with this command (which I found through Google):
/usr/X11R6/bin/xset dpms force off
Now I just click the icon on the toolbar, and my monitor goes straight to sleep.
(Now to fill out this patent application... "A single-click, software method for engaging display power reduction state"...)