Gamin MapSource Maps are the First Choice to Use with an eTrex Legend
This device comes with 8 megabytes of internal memory. With 8 MB of memory, you have the option to add more maps, details, POIs, or anything else from Garmin's MapSource Software product line. MapSource is the official resource for anything map-related that can be added to one of their GPS devices. This bodes well for not having compatibility issues since the software and the device are designed by the same company to interface with each other. MapSource software can come on a CD, and SD/Micro SD card, or you can simply download it directly from the Garmin website.
With the PC interface cable that comes with this model, adding new maps and data is a breeze. The eTrex Legend HCx uses micro SD cards which has plenty of room for downloading all you'll need. A 2G card can store a whole lot of the world on it. Built-in to the device, no matter what maps you're using, is the ability to designate 1000 waypoints/favorites/locations, make up to 20 routes, and store 10 saved tracks.
As far as what maps you can use from MapSource, the sky is literally the limit (actually the sky above the places they make maps for, they don't exactly cover the globe). They have their helpful road navigational software CityNavigator from many places such as Australia, the Middle East, and Australia, for example. Along with water maps for the Atlantic and Pacific, they offer inland lake maps for many of the Midwestern states in America such as Minnesota and Wisconsin.
However, since this is a portable GPS that if a favorite amongst the outdoor-inclined troubadours, it will be trail and Topo maps that are sought after the most. Garmin MapSource offers many good ones to include Topos for the U.S. Great Britain, Australia, and Morocco. They also have the National Parks of the U.S. laid out in great detail as well. For a complete listing of what is available for your Legend, visit Garmin.