France! As a Britsh and American couple we love cycle touring in France. Campsites everywhere, fabulous network of secondary roads, spectacular scenery, great cheap wine, and a lovely slightly slower pace of life.
We cycled from Brittany in the north west to Menton in the south east - a big adventure - if you look up Skedaddle's web site you can get an idea of routes. (they do loads of trips in Europe so good for inspiration for independent travellers). That trip took us about about 5 weeks, 1300 miles (we did not go a direct or quick route). First class. We included part of the Loire a Velo which is brilliant if you are looking for an introduction to cycle touring - fairly flat, good route maps and signage, and beautiful Loire countryside, towns and villages. And if you like mountains you can dip into the Alps or Pyrenees.
For shorter more concentrated pleasure - I think the area around Rhone Valley and east to Dentelles / Mont Ventoux / Gorges de la Nesque / Gorge du Verdon / Luberon villages provides some of the finest cycling anywhere - you can tune it to your abilities and it is absolutely spectacular.
Last year we cycled round (and across) Corsica - this was one of the best trips. A French Island, hilly in the centre (climbing up to a mile from the coast), French, and big enough to keep us happy for 3 weeks. Beautiful coast, mountains, villages, towns and beaches. We dipped into Northern Sardinia (Italian island) but didn't like it, on the whole.
France... Hmmm we go every year for about 5 weeks of cycling - we avoid the summer (mid July to Mid Aug) and find Aug / Sept to be ideal. Into October and it starts to get darker and less attractive for camping.
Ian