USAPhotoMaps is one of the coolest
pieces of (free!) software I've ever seen. It uses images from the MicroSoft TerraServer to
populate location information with satellite photos or topographical
maps. It interfaces with several GPS systems (such as Garmin or
anything that groks NMEA) and will show your current location, let you
send/receive waypoint data to/from the GPS unit, zoom in/out, scroll,
create routes to send to your GPS unit and lots of other things. This thing has it all and it's
free! If you're into maps or GPS (you don't have to
have a GPS unit to use it), this is a nice thing to have.