I use the Garmin 76map that fishincreek mentioned. I believe they have had an update since I got mine. Also got the HotSpots map CD with it. You get to unlock one region, or pay more to unlock another region. The region I picked has portions of KY and TN on it. The unit is pretty easy to use. The maps allow you to track your position on the map. If you zoom in, you can see the contours on the map. I read portions of the manual when I first got it, then went out on the lake and played with it. I recommend getting familar with the unit before you really need it (i.e., you get fogged in). Try it out on a slow fishing day. Easy to set way points and backtrack on a route. As fishincreek mentioned, it can save you from spending a cold night on the lake! I also find it usefull for setting way points on areas that look good during the day so I can find them real easy again at night. The unit also has highway maps preloaded. Usefull for when you travel. Probably other maps that can be added to the unit.

Andrew