Ran into the BusMonster site through a post by scoble (which weird as it is, I am not able to find a link to) and am just fascinated by what a cool little tool this really is. Really slick looking and functionally compelling at the same time.
A great example of the brave new world of web services that we are entering and how we can all build on top of each other and really leverage a variety of disparate technologies from various sources to build cool apps (this one for e.g. uses services from King County Metro Transit and the University of Washington Intelligent Transportation Systems Research Program among others and renders them using Google Maps).
Another example of maps and satellite images being overlaid and shown together can be seen here.