[Aug 22, 2009; Outdoor]
Using Google Maps overlays to visualize GPS recording is a pretty obvious idea,
but I'm too lazy to look at their API. A quick search revealed a site which offers this functionality:
It does not even require registration. A unique (secret) name for the uploaded track is enough to be able to edit or delete a track later on. Modifying the track after the upload turned out to be pretty easy. And this is what the result looks like: (last week's MTB tour)
It not only supports Google Maps, but also provides access to the mapping services of Open Street Map, Microsoft and Yahoo.