Google Map
Roadmap
http://mt0.google.com/vt/lyrs=m&hl=en&x={x}&y={y}&z={z}

Terrain
http://mt0.google.com/vt/lyrs=p&hl=en&x={x}&y={y}&z={z}

Altered roadmap
http://mt0.google.com/vt/lyrs=r&hl=en&x={x}&y={y}&z={z}

Satellite only
http://mt0.google.com/vt/lyrs=s&hl=en&x={x}&y={y}&z={z}

Terrain only
http://mt0.google.com/vt/lyrs=t&hl=en&x={x}&y={y}&z={z}

Hybrid
http://mt0.google.com/vt/lyrs=y&hl=en&x={x}&y={y}&z={z}

OTHERS:
Bing Satellite
http://ecn.t3.tiles.virtualearth.net/tiles/a{q}.jpeg?g=1

Esri Satellite
https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}

Esri World Topo
https://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/tile/{z}/{y}/{x}

CartoDB
https://cartodb-basemaps-a.global.ssl.fastly.net/light_all/{z}/{x}/{y}.png

Open Street Map
http://tile.openstreetmap.org/{z}/{x}/{y}.png