Are you serious?

The only one I can really think of (admittedly I'm not expert in this) is the Garmin Edge 705 with City Navigator, which is the same maps as the Garmin Nuvi sat-navs, it can do turn by turn directions on the road, or you can download maps offroad and follow a trace.

I'm pretty sure no one does a proper 'sat-nav' system with off road maps, although an increasing number of systems can show a decent base map with an overlaid route they can't tell you when to make turns and such.

at the moment, there is nothing that routeplans the way a car nav does off road, if you are going offroad the route needs to be preplanned, Personally I own a 705, but would buy an oregon toda.y

Most gps units can have routes uploaded using the gpx standard.