Do you mean on TV or actual spots along the route of the tour?
If you mean on TV, Eurosport has a great daily coverage of the Tour (in English, of course) which includes a live coverage of a big part of daily stage (most of the stages covered, unless there is some other exceptional event in that day), a ~30 minutes daily "behind the scenes" show and a daily summary of about an hour around midnight. The Eurosports' team is pretty professional and knowledgeable and usually very enjoyable to listen to.
If you meant to actually go to the Tour's route and watch the stages live, then I guess you should start with viewing this year's route at the official Tour site (there is also a nice flash map there). There is a detailed information on all stages, starting/ending points and climbs.
Good (and very crowded) hot spots would be: towns at the end of each stage, peaks of any major climbs, a combination of the previous too would be high popular (like on stage 8) and of course, the grand finale on the Champs-Élysées.
Enjoy the Tour!
