I need a way (possibly a third-party application) that allows me to use maps and GPS without an Internet connection. I don't use it by car, just for walking in cities. It would be nice if I could just copy all data relative to a particular city before going there for tourism. The Google Maps app does not store maps reliably, so it is risky to rely on it without an Internet connection.

Google Maps is great, but unless you have an unlimited data plan, it's going to cost a lot downloading all that data all the time. Do you know of any (preferably free) good offline map application for Android? Ideally one that can do navigation (preferably with voice) and in my location (Sydney, Australia).

I have a few use cases for this - running or walking to track distance and time, hiking to know if I'm backtracking on myself, and driving aimlessly (well, when gas prices are cheaper than they are now) around an area to explore it so I know places that I've already been. I did a quick look around the market and nothing stood out. Does something like this exist?