I regularly use Locus. It doesn't have much in the way of navigation support (although I think this is in the works), but for off-road and off-line use it's fantastic.
It allows downloading of maps for off-line use, supports SQLite and GEMF maps, which allow large map (2GB limit for SQLite, no realistic limit for GEMF) tile sets on your SD card without wasting masses of space. It also supports vector maps as well as bitmap ones (more coverage, less disk space). It has a very good interface and is well supported.
There's a free version with ads which doesn't support in-app map downloading (I think), although you can use your PC to download the maps. The paid version is not expensive.
That all sounds excessively glowing, so I should emphasise that I'm not the developer and have no affiliation; just a very happy user!