Google's Geo Developer blog posted about five great maps developed based on Google Maps API. The list includes the renowned photo sharing tool - instagram's app called InstaEarth, which makes use of the to help users discover instagram photography in a map.
InstaEarth Another interesting application that uses the Google Maps API is the Submarine Cable Map from TeleGeography which makes use of the to generate map layers of submarine cable routes. The map also uses to customize the standard Google base maps for better visualization of the cable routes.
Check out the rest three here