The big question is who is gong to be the first to combine a live feed of the cyclists in the Tour de France with the new Google Maps street view of the race route, to give us a first person view of the yellow jersey? In theory it should be easy to do, as long as you can lay your hands on a live geo-feed of the race.
Ubilabs last year produced an excellent Google Maps mash-up tracking the position of the cyclists in the Tour de France live on a Google Map.
Polar, a company that seem to sell watches that track your physical performance, have a live tracking map of two cyclists in France. I assume that this is a test for the race itself and that they will be following the race live. The map page says "Next stage starts at 2008-07-05 12:30 French time", so it looks like they will be following the Tour de France.
When the two test cyclists aren't riding the map switches to a Flash animation.
Inway have a very nice map of the Tour de France route. Each stage of the race is shown on a Google Map. You can navigate between the various stages via links in a sidebar. The map seems to have been built using the Google Maps Flash API as there is some nice morphing between stages.
Mapstars have a very similar map that shows each of the stages of the race on a Google Map. Mapstars have colour-coded the polylines for each stage depending on whether it is a mountain stage, a flat stage or a time trial.
Hotels-in-France has embedded a Google Map for each of the stages of the Tour de France alongside a description of the stage.
Bikemap have also created Google Maps for each of the Tour's stages. Each map is accompanied by an elevation graph of the stage and with details about the stage's distance, vertical climb, inclination, and road surface.