I recently spent a long weekend near Narbonne in the South of France. London to Narbonne return was a dream by train. Eurostar to Paris, an easy transfer on the RER between Gare du Nord and Gare de Lyon and 300kph all the way on the TGV. I didn't book more than a month in advance and still got good deals. Go to http://www.tgv.com, click on France on the map and choose English (if you click on the UK, you get transferred to Rail Europe, which isn't as good). I got first class both ways for ?106, which added to a first class journey back on Eurostar with a meal and a litre of red all added up to a far more civilsed and green alternative to SleazyJet or Ryan Unfair. I would heartily recommend it.
It's a shame that our overpriced and chaotic privatised rail companies weren't run by SNCF, NMBS, D Bahn, NS or any of our mainland European neighbours. However, we seem in the grip of a collective political madness of public bad, private good. Hey-ho!