This tip should prove useful to people who utilize two screens during their workday, especially those who give a lot of presentations!
Disclaimer: This only works in Windows 7.
This first option will turn off your secondary screen completely.
This second option will duplicate your two screens, which is most useful when connecting to a projector or when you have a customer sitting across your desk whom you have a monitor pointed at.
This third option extends your desktop across both screens, which is the most commonly used setting for people who work with two screens regularly and just want the extra real estate.
This fourth and final option is simply the inverse of the first option, and will cause your second screen (or projector) to be the only screen shown.
Hopefully this saves you a few clicks and a lot of frustration!