Yahoo recently released an official AS3 API for Yahoo! Maps, which provides another option for Flash-based GIS applications. This adds to Mapquest’s official AS3 API and a couple of partially-complete, open source AS2 APIs for Google Maps.
All of these services provide the traditional AJAX APIs, of course, and that’s perfect for a lot of uses. By using Flash as the rendering engine, though, there are new options available for the developer. Things like incremental scaling between tile sets, map rotation, and more advanced multi-level vector and raster overlays immediately come to mind.