I know that you can swipe from the top and turn wi-fi on or off, but I turn it on and off manually a LOT, so I wanted a button on the home screen I could use to spare myself the extra swiping up / down. The widget uses a global variable so that the icon / label will properly update even if you do turn wifi on or off one of the many other places you can do so.
Download the three files below, and import them to your device. To add the button to your home screen, long-press on an empty spot on your home screen and select Widget. Select Task (with the Tasker icon). On the tasker screen, select the WiFi_Toggle task. Hit the green checkmark to save your new widget.