Probably depends on what you are looking for. I have a GPS 76 I got used. Came with a street map and I bought another chip for it so I can load up topos. I got some free topo maps here-http://www.gpsfiledepot.com/
Here is another Garmin related site-http://gpstracklog.com/2009/09/free-gps-topo-maps.html
I'm sure there are others, but these two should be a good place to start. GPS depot has some good forums and helpful posters as well. I'm a GPS newbie too, so they were helpful. You can buy commercial maps, but they tend to be pretty expensive.