Script

jQuery(function($){
    var passInput = $('#password');
    var passVisible = $('<input type="text" value="" name="password" id="password_visible" />');
    var passCheck = $('<input type="checkbox" />');
    passInput.after(passCheck);
    
    passCheck.click(function(){
        if(this.checked){
            passInput.replaceWith(passVisible.val(passInput.val()));
        }else{
            passVisible.replaceWith(passInput.val(passVisible.val()));
        }
    });
});

Demo