Terrabrowser

Terrabrowser is an internet browser for satellite photos and topographical maps which are obtained from the Microsoft Terra Server web site.

The map data is provided by the U.S. Geological Survey (USGS) and therefore only covers the United States at this time (although expansion to other map servers may occur in the future). Although a GPS receiver is not required to enjoy Terrabrowser, using one opens up more extensive features such as bookmark transfer, tracklog and route display, and live tracking*. Includes extensive bookmarking support, tracklog/route rendering, image cache, address search, region download, and many other features!
Terrabrowser features built in support* for serial based Garmin GPS receivers, and also supports Magellan receivers when combined with the freeware program MacGPS Babel). Download waypoints from your GPS to display on the maps, edit them, upload new waypoints to your receiver.
Terrabrowser aims to be compatible with the rest of the GPS world, so it uses the XML based GPX file standard which allows easy exchange (file, copy/paste) with other GPS programs for Macintosh, Linux, Windows, etc. which support this format. The NMEA standard protocol is also supported* which allows for a "live tracking" mode to display the user's realtime position on a satellite map (cached or not).