I know that there are many schools of Horse Riding, such as Natural Horsemanship, founded by Pat Parelly (USA, Western riding), Haute Ecole, James Phills school, German and Franch schools
I certainly would not say Natural Horsemanship was founded by Pat Parelli. NH has been around a lot longer and with names attached to it long before PP. Western riding itself was born out of necessity to work in the open country mainly working cattle.
But in the more "world riding" the SRS and CadreNoir are right up there.
Whilst Parelli didn't invent NH, he is one of the largest NHs out there. And he doesn't do just western either, his wife is a top level dressage rider. As for world schools, Mark Phillips Equestrain center!
Theres Meredith Manor! Its in either Virginia or West Virginia, I can't remember. My trainer went there and is a riding master 6 graduate. She also got her level 2 teaching certificate and was invited to teach classes there but came back to my stable =]