Animation effects for menu items
I assume you have set up the links in the menu properly, i.e. they reference the elements they correspond to, something like

&lt;ul id="menu"&gt;
    &lt;li&gt;&lt;a href="#home"&gt;Home&lt;/a&gt;&lt;/li&gt;
    &lt;li&gt;&lt;a href="#referenzen"&gt;Referenzen&lt;/a&gt;&lt;/li&gt;
    &lt;!-- ... --&gt;
&lt;/ul&gt;


So you can just search for the corresponding link with the attribute selector [docs] and get the enclosing li element:

$('#home, #referenzen, ...').bind('inview', function (event, visible) {
    var $menu_element = $('#menu a[href=#' + this.id + ']').closest('li'), 
        // get the '#nav li' element at the same position 
        $nav_element =  $('#nav li').eq($menu_element.index());

    $menu_element.stop().animate(
        {backgroundPosition: visible ? '(0 0)' : '(-200px 0)'},
        {duration: 500}
    ).find('a').css({color: visible ? 'white' : 'black'});
    $nav_element.stop().animate({opacity: visible ? 1 : 0.2}, 500);
});


If you don't have set up the links correctly (you really should), give the li items in the #menu (and maybe #nav) list a (for example) data-id attribute with a value corresponding to the element's ID and again, use the attribute selector to get them.