Jaime Lerner reinvented urban space in his native Curitiba, Brazil. Along the way, he changed the way city planners worldwide see what's possible in the metropolitan landscape.
http://www.ted.com/index.php/talks/jaime_lerner_sings_of_the_city.html
I saw him give a lecture at OU last year. He's a great speaker and a lot of his ideas on sustainability and especially mass transit are excellent.