The Rino's by Garmin are nice if your hunting partner/party has them as well because you can see where everyone is at.
Like Bob mentioned some companies offer a service you can subscribe to that will allow you to get specific maps, or your other option is to purchase map software. Just be aware of how much memory or memory capability the gps has, as this will determine the amount and size of the maps you can upload to it.
If you are just looking for something that you can use to navigate with while out in the woods, and occasionally mark waypoints (wallows, springs, landmarks, etc...) an inexpensive baseline model will work. If you want something that doubles as a 2-way radio the Rino's are awesome. My wife bought me one last Christmas. They are great units.
BowHuntr