Google Maps is the clear choice for iOS, but it does lack one key feature found in its Android counterpart: the ability to save maps offline. If you need that feature on the iPhone right now, right now GPS Navigation 2 is having a sale on both its app and the downloadable offline map for Australia.
The app itself is on sale for $0.99 rather than $1.99, but the big saving is on the downloadable Australian map, which is usually $5.49 but has been reduced to $0.99 as well. The navigator uses the crowdsourced OpenStreetMap project, so the coverage in rural areas might be variable. If you give it a try, tell us how it works for you in the comments. The deal runs until December 28.