Travel by GPS has released their first Tour Guides for compatible Garmin GPS devices. The initial releases feature Huntsville, AL, and Asheville, NC — my former home, billed here as the "Paris of the South." Okay, I am biased, but I often describe it to people as a very cosmopolitan city.
This is the first third-party application like this that I have seen. Doug Adomatis, the guy behind Travel by GPS, has been wanting an application like this for years. He notes that his is the first site to publish free Garmin tour guides in the GPI format. This format is "compiled from a special version of the GPS data (gpx) file which links audio (mp3) files and image (jpg) files." The MP3 files play as you approach an included point of interest (POI).
Compatible Garmin units: