I would vote for Germany, Spain and Greece. In Germany, it is not uncommon to see naked people in parks even in city centres (Munich, Cologne and most notably the capital, Berlin). Most of the lakes and rivers in Berlin and at the Baltic sea are clothing optional, and in saunas, it is not even a question whether you should take off your bathing suit
http://active-naturists.blogspot.com/2008/07/active-naturists-in-berlin.htmlSpain has lots of nudist beaches too, including a couple in central locations in Barcelona; I took part in the world naked bike ride in Madrid, and all people on the streets seemed to be fine with that – we even went to buy water and food naked!
http://active-naturists.blogspot.com/2009/06/world-naked-bike-ride-madrid-2009.htmlAnd although Greece doesn't have too many 'official' nudist beaches, nudity is tolerated pretty much anywhere outside urban areas.