Take a look at MapCruncher. A very interesting new map mashup technique from the folks at Microsoft Research. It basically allows you to overlay any digital map image on top of a normal, zoomable Virtual Earth map.
Created in 2006, Big Art Mob's original purpose was to accompany the Channel 4 show, 'Big Art Project'; the goal being to create the UK's first comprehensive map of street art. The site is now being re-launched along with iPhone and iPad applications, inviting users to upload and map public art anywhere in the world.