I really like my Garmin Rino 530, it has GMRS/FRS radio capability, NOAA weather updates, and built-in temp and altitude. GMRS radio range can be as great as 8-10 miles in the right conditions, making this feature very usable out sledding. It also has peer to peer locating; when another Rino user keys their mic on their radio, their location shows up on the map on your radio. That is a very cool feature when you are sledding and someone is lost or stuck, or out in the woods with friends and you need to keep oriented to where the others in your party are. Battery life is excellent, I have gone as many as 18 hours on one charge. Bad side; there's no external antenna so use inside a vehicle is somewhat limited.
Magellan Explorist is a nice unit as well, I like the topo-3d software Magellan has better than the topography software I purchased with the Garmin.
When I was looking, I decided I did not want one that mounted to the sled because of the other activities I do in non-snow conditions. I use it more in the summer than in the winter; for me, a mountable unit did not meet my needs as well.
For a LOT of info, go take a look at the GPS store.
http://thegpsstore.com/
I purchased a Magellan through them, then had problems with it, and decided on two Rinos instead. Good service, no nonsense return, I would do business with them again.
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Rebuilding the fleet!
2008 RMK 600 155", 2006 RMK 600 144", 98 Indy 440, 95 Prowler 550 2-up, 1990 Indy 650
RIP, destroyed by fire 1-22-2008

04 RMK 800, 05 RMK 600, 02 RMK 800, 97 RMK 700