Equally Spaced, Variable-Width Navigation Links

flex-full-width-nav-css2.css

ul {
    display: table;
    width: 100%;
}

li {
    display: table-cell;
}

a {
    display: block;
}

flex-full-width-nav-css3.css

ul {
  display: box;
}

li {
  box-flex: 1;
}

full-width-nav.js

(function($) {
	$.fn.justifyNav = function() {
		return this.each(function() {
			var $this = $(this),
				$children = $this.children(),
				containerWidth = $this.width(),
				linksWidth = 0,
				count = $children.length;
			$children.each(function() {
				linksWidth += $(this).outerWidth();
			});

			// Don't give the last item or the 2nd to last item any right margin, then float the last item right. 
			// This will account for small errors in JQuery's calculation of the item widths. 
			// Otherwise the list can overflow the container!
			var linkSpacing = Math.floor((containerWidth - linksWidth) / (count - 1));
			$children
				.css('margin-right', linkSpacing + "px")
				.filter(":last")
					.css({"margin-right":0,"float":"right"})
					.prev()
						.css({"margin-right":0});
		});
	};
})(jQuery);

justify-full-width-nav.css

#nav {
  text-align: justify;
  min-width: 500px;
}

#nav:after {
  content: '';
  display: inline-block;
  width: 100%;
}

#nav li {
  display: inline-block;
}