Android: The Wifi Toggle Widget turns your Wi-Fi connection on or off with the press of a single button, rather than navigating through a bunch of screens.
To install, head over to the Android Market, search for "toggle wifi", and install the widget to your home screen. Once you've completed those simple steps, you can toggle your Wi-Fi connection on or off with a single button press, very useful for saving battery life when you don't really need the wireless capability enabled. If you don't mind an extra button press, you can use the previously mentioned Useful Switchers application to toggle a bunch of settings at once.
Hit the link for the full screenshot tour, or check out a dozen super-useful (and free) Android applications.