LookBackMaps is a collection of historical photographs that can be compared to the same current view as seen on Google Maps Street View.
The photographs are geotagged and displayed on a Google Map. Users of the map can select a date range for the photographs that they wish to view. To view a photograph alongside the current Street View just click on any of the pictures inside the information windows.
To add your own historical photographs to the map you just need to register with LookBackMaps.
Utrecht van Boven - historical photos of Utrecht on a Google Map
Sydney Sidetracks - a map of audio, video and photographic records of Sydney's past
HistoGrafica - historical photographs on Google Maps
Virtual Time Travel - archive film of locations. Unfortunately some of the YouTube videos on this map have now been removed, although many of them still work.