Google have added the Elevation service to the Maps API for Flash. Maps API for Flash developers can now add elevation profiles to their maps. As an extra bonus the service comes with a cool 3D twist.
The Google Geo Developers Blog has a great example of the elevation service being used with driving directions. In the example you can see the 3D feature in action. If you mouse-over anywhere on the elevation profile the map will zoom to your location and rotate the map to face the direction you should be facing if you are following the directions.