Just upgraded my Navman software on my ipaq with Navigator 2 from Tom Tom - it's a big improvement for me. The main things is that you can have custom overlays, and that they have a sdk that can be used to create neat utilities that can talk to the sat nav. So I now have the uk speed camera database on the Tom Tom software has been extended to warn me when I'm approaching a camera - neat. And I can find a wi-fi spot anywhere in the country!
What it doesn't have is traffic information. So I am looking for a web service that would provide live traffic information. TrafficMaster don't appear to offer that as a service, so if anyone knows of one, then please let me know.