The TDF site now has an official link to the Google Earth file of the Tour route.
Now you can also track the race in progress directly in Google Earth, with a live link showing the situation of the race along the route. I'm not so sure how well this will work for tomorrow's Stage 7 Time Trial, but it sounds like fun, anyway. The link and how-to explanation can be found here.
Here's another site which allows you to track the position and vital statistics like heart rate, speed, stress and power of a few selected riders who are using special equipment on their bikes allowing this information to be transmitted. With accompanying blog explanation.