London was perhaps the most influential city for 60s male fashion because it was the Center of the whole world during most of this decade. The continous exchange of its artists and creative geniuses led to the establishment of a new culture, a new phase in man kind history. Paris was still the capital for womenswear, with designers such as Chanel, Balenciaga, Dior (with Marc Bohan), and a young yet very talented YSL (it was during this decade that he reached inmortality with his A shaped Piet Mondrian dress) kept amazing women worldwide. Of course I can't forget to mention Mary Quant, from London, who invented the mini skirt and caused a worldwide revolution.
Men, especially young men, were looking for a new style, tired of the "old" and classic styles that had already been worn and used for decades. London had that new modern and youthful look. This new fad in men fashion was influenced by many elements that came from different time periods and cultures...It was possible to find medieval style shirts, lace shirts that embodied the Romantic look, Hindu inspired suits, Mao neck shirts and jackets, big medallions that had the shape of Military orders to accesorize the look, bellbottoms, and of course the whole Mod look. So as you can see there were many options back then for men, and the place to find all of these items was the legendary Carnaby Street. This was a trend setting point, trends for both women and men fashion of the 60s were defined here, if it was "in" here, it would likely be "in" worldwide.
Carnaby Street may still remain as part of the 60s cultural legacy, but what is true is that nowadays and since almost 40 years ago there hasn't been another Carnaby Street. I think that the modern "equivalent" of this street can be the Internet's fashion sites, forums, and blogs where styles and trends are discussed...but still it's not the same.