I'll be installing a Pioneer Nav unit in a few weeks (most likely anyway). As for off roading, get a Garmin 60CSX. This unit is amazing. Small 2.5 inch screen but you don't need to plug it in, it last for 14+ hours with rechargeable NiMH batteries.
Not a road router, but a GPS designed to hike with, and with the car mount, you can't get lost anywhere. Has the reverse track feature (breadcrumbs) to lead you out.
Uses the new SiRF III chip, and latches onto the satellites (including the WAAS satellites) faster than any GPS I have ever owned.