We have found this to be a very full-featured and capable nav program for the iPhone 3G or 3GS. Weighs in at 1GB but it has a great many features and works very well. Highly recommended. 

With the NAVIGON MobileNavigator you can transform your iPhone into a fully functional mobile navigation system that is every bit as good as the multi-award-winning personal navigation devices from NAVIGON in terms of its user-friendliness and features.
Thanks to a faithful adaptation of the menu functions, the NAVIGON MobileNavigator fits in seamlessly with the operating concept of the iPhone. The application includes the latest map material from the market leader NAVTEQ.