Found this blog post listing the 15 most cycle-able cities in the world on the Matador Network. They were not ranked, just listed as the best for their area. It was more a list of European and North American cities than a true world listing, but still interesting.
It would appear to just be the opinion of the blogger, not a true scientific study, but it is interesting to note that Perth wins the title as the most cycle-able city. This is surprising as it is not the best performer when it comes to mode share for the journey to work (data from the Cycling Resource Centre).
The 2006 census shows Perth coming in with the 3rd worst mode share for cyclists to work (same mode share as Brisbane) and lagging far behind Canberra and Darwin. Does that make Darwin and Canberra the most cycle-able cities? Or is it just that they are the cities with the worst public transport and parking issues?