TGV - High Speed Train
The TGV (Train Grande Vitesse) started in 1981 with the Paris - Lyon line. Twenty years later, from 10 June 2001, the Lyon - Marseille section of high-speed track opens and you can travel from Paris to Marseille in 3 hours. London to Marseille now takes 6 and a half hours.
The Marseille-Nice section of the line still uses the standard rail system, at the standard speeds. There's some lovely scenery along the coast better appreciated at the leisurely pace, but the trip takes two and half hours, making the total Paris - Nice time 5 hours 30 minutes.
Reservations and Tickets.
You can reserve your seats and buy your tickets directly from the SNCF website. You have the option of reserving your seats via the web, and paying for your tickets later, at the station. The train stations (gare SNCF) in the larger towns have kiosks where you can purchase the tickets.
When you make your reservation you can order a meal for the trip (we haven't tried this, so don't know exactly what you get). On the TGV trains you can sandwiches and such things at a buffet car.
A reminder from Mark Venot,
"You should indicate the cost to park in those new stations since it's rather stiff (even by the cote d'azur standards)."