Just finished reading Keith Peter's ActionScript 3.0 Animation book, and I very highly recommend it. Chapter 4 is all about pathfinding using A* but is based on a tiled grid network. So I adjusted it, in such a way that the nodes and arcs are derived from street features off a shapefile. The resulting application enables you to select a starting and ending street intersection and a path is displayed. In addition, you can add street barriers so that the calculated path will go around the defined barriers. The nodes and arcs are spatially indexed. This enables live reverse geocoding as the mouse moves - that means that once the mouse is close enough to a street segment, a snap point is calculated and based on the side of the street, an interpolated address is calculated and displayed. Check out the application here, make sure to zoom in to enable snapping and path finding. Again, once you move close enough to a street segment, a snap point is displayed and the address is displayed on the top right corner. You can type the 'x' character to toggle the street as a barrier. Upon a mouse click, the closest node is selected as a starting node. Next, move the mouse to another node and click, and a path is displayed. The last selected node is now the starting node, click again and a path is calculated and displayed. Type 'C' to clear the resulting path. Like usual the source code is here. Have fun.
PS: People have reported some drawing issues :-( that have been resolved if you use FP10.