I've posted this link before, but you may not have seen it, jignall. A very experienced couple's top 25:
http://www.ridetheroad.com/web/world.aspx

As for my favorites:

SW France, especially Lot & Dordogne valleys
northern Thailand (Chiang Mai-Golden Triangle area)
Corsica
south-central Chile (Lake region) & adjacent Argentina
Tasmania
Rocky Mountains (tour from Denver, Colorado to Jasper, Alberta), USA & Canada
New Zealand
Cape Breton Island, Nova Scotia, Canada
Hawaii (all of Kauai, all of Maui, and windward side of the Big Island)
west coast of Scotland & Scottish highlands (but I had sunny & warm weather, which isn't likely to be repeated anytime soon!)
Michoacan, Mexico
just about anywhere in France not listed above except for area directly between Paris & Belgium