Surprised Madison isn't on there as a boy name that became a girl name. It was a traditionally male surname (eg Madison, Wisconsin, the state capital, was named after James Madison) until the 1984 movie Splash, where a woman has to make up a name, looks around, sees a street sign for Madison Avenue, and says her name is "Madison". That was understood to be a joke at the time, akin to someone calling themselves Broadway, but because of that movie it quickly became a popular female given name. Personally when I was choosing my name, it came down to between Madison and Madeline, and the traditional masculine association of the former tilted me towards choosing the latter