Proto.io, a mobile prototyping service, has created a handy generator for quickly creating on/off flipswitches.

The switches are built with pure CSS3 and it is possible to customize the look completely.

CSS3 On/Off Switch

It also comes with pre-defined styles for iOS4, iOS5 and Android as well.

P.S. In order to add functionality to such a control, it would be a good idea to listen to the "state" of the switch and add our custom events accordingly.