Shortcut to turn Wi-Fi on/off on Samsung Galaxy Nexus?
On the Samsung Galaxy Nexus, you can add the Android built-in "Power Control" widget to your screen, this has a one-click button for turning Wifi on and off on the left-hand end of the bar.



(screen shot is from the home screen of my Galaxy Nexus, but this power bar has been built-in to Android since at least v1.6, though some manufacturer customizations do remove/change it)

To add this press the circle-with-dots-in icon at the bottom of the home screen to go to your apps list, then select the "WIDGETS" tab at the top of the screen and scroll along until you see "Power Control" or "Settings", hold your finger down on that and it should allow you to drag that to an empty spot on one of your home screens.

Also, if you've received the Jelly Bean 4.2.1 update, it contains a quick settings menu that allows you to get right into the Wi-Fi page in settings. You can swipe down with two fingers from the notification bar, or swipe once and click the button in the top righthand corner.



Then you long-press on the Wifi icon to turn it on or off.