Based on Jason Weaver's FlexNav. Changed to suit my preferences - on large screens the items in the nav are floated left rather than like buttons, acting more like a regular ol' fashioned drop-down. Added support for non-javascript devices on large and small screens.
Add flexnav.css to the head of your document
<link href="css/flexnav.css" rel="stylesheet" type="text/css" / >
Add jQuery and jquery.flexnav.js to the head of your document
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script type="text/javascript" src="js/jquery.flexnav.js"></script>
Initialize FlexNav right before your closing body tag
<script>
$("flexNav-nav]").flexNav();
</script>