Found this and thought it looked interesting. I saw it at http://test.cita.illinois.edu/aria/tabpanel/tabpanel2.php#lsc1 and in that page they cite "ajpiano on the jQuery forums." Untested but seems sane

focusable

// focusable is a small jQuery extension to add a :focusable selector. Credit to ajpiano on the jQuery forums.
//
$.extend($.expr[':'], {
    focusable: function(element) {
      var nodeName = element.nodeName.toLowerCase();
      var tabIndex = $(element).attr('tabindex');

      // the element and all of its ancestors must be visible
      if (($(element)[(nodeName == 'area' ? 'parents' : 'closest')](':hidden').length) == true) {
        return false;
      }

      // If tabindex is defined, its value must be greater than or equal to 0
      if (!isNaN(tabIndex) && tabIndex < 0) {
        return false;
      }

      // if the element is a standard form control, it must not be disabled
      if (/input|select|textarea|button|object/.test(nodeName) == true) {
        return !element.disabled;
      }

      // if the element is a link, href must be defined
      if ((nodeName == 'a' ||  nodeName == 'area') == true) {
        return (element.href.length > 0);
      }

      // this is some other page element that is not normally focusable.
      return false;
    }
  });