I used Navfree during my brief stint with Android last year. It has mixed reviews but I was happy with it. It uses OSM maps and allows you to download maps for whole specific countries. The maps do not even take too much space*), yet provide more detail than my TomTom**).


*) IIRC, the UK took something like 380 MB, but it was nearly a year ago so give or take 50%, shall we?
**) A dedicated satnav device that is, not a TomTom app.