Hope this isn't a double post. I'm, obviously, not affiliated w/ the app. Gizmodo reviewed it pretty well, if I recall correctly. It's not probably not quite as nice as Navigon, but for $20 bucks, it's a steal (imho). 
http://itunes.apple.com/us/app/copilot-live-north-america/id324327451?mt=8
http://itunes.apple.com/us/app/copilot-live-north-america/id324327451?mt=8
