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.
Following-up on yesterday's post on the best new mashups, here is another notable mashup from this past week, yesterday's Mashup of the Day: Gaiagi Driver. What is it? It's a mashed-up 3D driving simulator that uses a lot of web APIs across multiple windows to create a unique driving experience. Give it a starting and ending address and it follows the path created by the directions and shows your present position in four different views: