KML layers

GMaps.js allows to add KML and GeoRSS layers:

infoWindow = new google.maps.InfoWindow({});
map.loadFromKML({
  url: 'http://www.searcharoo.net/SearchKml/newyork.kml',
  suppressInfoWindows: true,
  events: {
    click: function(point){
      infoWindow.setContent(point.featureData.infoWindowHtml);
      infoWindow.setPosition(point.latLng);
      infoWindow.open(map.map);
    }
  }
});

Note You can learn more about KML and GeoRSS layers here.