Is there anything like a directory or list of notable leading living figures based on subject area or research concentration?
I think the American Academy of Arts and Sciences might be a good place to start, at least if your focus is primarily on academics in the U.S. Two criticisms of the academy: it tends to be clique-y. Harvard is always going to have the most new fellows every year because they've already got the most fellows. Second, not everybody who deserves to be a member is one. They're really good about not giving memberships to people who don't deserve them (at least in my field, Philosophy), but there are some people who clearly should be members but aren't.