Navfree GPS

This application is pretty good, considering its free, and seems to be actively improved upon as we speak.

Presently you may need a data-connection to search for addresses, however the map data is offline, stored on the phone.  For different countries/regions search facilities while offline are cropping up with updates to the app.

Google Market: Navfree GPS

So far, initial impressions are that the GPS on the phone is not that stable so the map jumps around a lot, especially when stationary.  In comparison to say the Garmin Nuvi 250 or 320, the maps are similar but the routing and stability of position is not as consistent.

Visually, the maps look great and there is a nice feature where you can fix map errors.  This feeds into the openstreet foundation map data-set.