Offline Map/Navigation App for iPad

I am looking for a map/navigation app that will work with a wifi only iPad and that stores the maps on the iPad. I understand that the wifi only iPad will not be able to do true navigation as it lacks GPS. Essentially, I am looking for something that would let my iPad replace the slew of paper maps/gazetteers I keep in my car.

I may be getting an iPhone in the future so a GPS capable app would not necessarily be a waste of money.

Any suggestions?

Thank you.