While I didn't fully explore the possibilities, I found a pair that
meet my needs. Yes, a pair.

First. Most GPS nav systems are oriented towards providing directions
from one place to another. They may have additional information
(restaurants, hospitals, etc.) They usualy won't have forest roads
(fireroads).

The two that I got were due to >MY< needs, which may be different
than yours.

1) Bluetooth GPS. Several models are available. I choose GlobalSat
BT-338. Note, there is no display on this. It is ONLY a GPS module
with bluetooth connectivity to a computer. Battery life is purposed
to be up to 13 hours on a charge. It came with AC and DC adapters to
recharge it's internal battery.

1a) Software. I bought MacGPSPro. This is for a Macintosh computer. I
also bought pre-calibrated USGS topo maps for most of the NE US (a
lot of these are also available for free download, but I didn't want
to spend the time getting all). In combination with the BT-338, this
software lets me see (on 7.5' quads) where I am and what's around me.
Works great with my 12" Powerbook.

2) Pioneer AVIC-N2, in dash GPS Nav (6.5" screen). This is a DVD/CD/
GPS Nav/AM-FM unit. It is XM and Sirius ready and also supports an
iPod interface. (iPod and Satellite radio are extra cost items, GPS
is included). Not cheap, $2000 or there abouts un-installed.

The GPS Nav software is very good. Maps are accurate and fairly up to
date. One DVD of Eastern US and Canada, One DVD of Western US and
Canada (some overlap between the two). The Sirius and iPod interfaces
aren't so good. They work, but are a bit clumsy.

GPS antenna is a magnetic mount. I put mine up under the luggage
carrier, just like my Sirius antenna. Works fine.

I did my own installed and it took quite some time. The Pioneer comes
with a remote box, in addition the DIN head unit. My remote box is in
my Westy's sink/stove cabinet. Part of what took so long was routing
cables for all the little stuff (antenna's, power, brake, backup
light, etc.)