For the Appalachian Trail:
http://postholer.com/gmap/gmap.php?trail=at
This map represents the entire Appalachian Trail in the greatest possible
detail. You won't find anything else like it on the web. It's the next best
thing to having Google Earth or mapping software installed on your computer.
It uses Google Maps, with Satellite, Topo and Hybrid maps available. And if
you're a Pacific Crest Trail fanatic, we've got the PCT as well:
http://postholer.com/gmap/gmap.php?startZoom=5
These are currently in the testing stage and we hope to base some really
exciting new features on them.
-postholer