Use Stamen's map tiles in your favorite mapping library, Google Maps version

GoogleMaps.js

// replace "toner" here with "terrain" or "watercolor"
var layer = "toner";
var map = new google.maps.Map(document.getElementById("element_id"), {
    center: new google.maps.LatLng(37.7, -122.4),
    zoom: 12,
    mapTypeId: layer,
    mapTypeControlOptions: {
        mapTypeIds: [layer]
    }
});
 
map.mapTypes.set(layer, new google.maps.StamenMapType(layer));