EarthNC.com, best known as a source for nautical data, has announced a new service and website -- TakItWithMe.com, which allows you to transfer Google Maps data and KML files directly to Garmin receivers, or download them as GPX files. The site utilizes the new Garmin Communicator plugin.
I just gave it a try and it worked very well. Output can be downloaded as waypoints, tracks and routes. The team there has put together a great video (shown below, after the jump) that does an excellent job of showing you how. It's really pretty simple.