With the latest WP OSM Plugin version some new tiles have been added, you can choose these maps in the shortcode generator. Have fun to add them to your site!
<OpenStreetMap>
<OpenCycleMap> <= API key
<LandScape> <= API key set
<Outdoor> <= API key set
<OpenSeaMap>
<Stamen Watercolor>
<Stamen Toner>
<Spinal Map>