Million Marker Map
The Million Marker Map uses 'Spatial DataBox' (SDB) to show over two million map markers on one Google Map.
The Spatial DataBox is able to perform 10,000 queries per second, and can return millions of markers per second. The 'Full Screen Map' button, situated at the top-left edge of the map, expands the map to occupy the full view of your computer's screen.
FindByClick.com is another example of a Google Maps mashup built on top of the Spatial DataBox. FindByClick is a community mapping site that lets users tag and share their favourite places.
Both the maps use the Google Maps API for Flash.