For anyone travelling on the French toll roads, I'd thoroughly recommend getting a Liber-t tag from http://www.saneftolling.co.uk . We've just got back from Nice and it saved us loads of time on the autoroutes. The look on the faces of French motorists as we cruised down the automated 30kph Liber-t lanes was priceless. They obviously thought we had gone down the wrong lane but when the barrier lifted and we sailed through we were the ones laughing! We had a tag a few years ago that we got from Sanef in France but to get a new one in France you now need to have a French bank account - they are still allowing existing customers to pay by credit card but the doors are closed to new subscribers and payment by credit card is due to be phased out altogether by the end of 2012. The Sanef UK service requires you to pay from a UK bank account by direct debit.
I ordered a tag late Tuesday afternoon and it arrived Wednesday morning - I can't praise Sanef UK enough for their customer service as it has been excellent. We're off to Bordeaux in September so will definitely be using it again.