You can use Google Maps to plot trails. Check out this link if you don't know how to use the My Maps feature of Google Maps.
To export, you can get the KML by clicking the "View in Google Earth" button on your map and save the KML data.
Another easy method to export your maps is to put them in a Google Fusion table, by using this utility:
This will ask you to authenticate your Google Maps and Google Fusion Tables accounts, but once you do, you can pick which maps to transfer to Fusion tables, or just download the KML file.
Once your map data is in a Fusion Table, you can click the "Notes" button for each trail under the "Geometry" column to view the GPS data.
You could also use Google MapMaker to make your trails available to everyone on Google Maps