In my opinion, the future of American is the 1992 birth year in general. It has awesome depth.
Ryan Harrison, Andrea Collarini, Denis Kudla, Jordan Cox, Jack Sock, Evan King, Bob van Overbeek, Mitchell Frank, and Daniel Kosakowski, among others.
Kosakowski increasingly seems like one to watch. Harrison, Cox, Kudla, Collarini, and Kosakowski form the top tier of the '92s in my mind. I'm not sold on Van Overbeek yet, despite the great tournament. King and Junior Ore are a couple guys who could be solid after a few years of college.
Edit: I forgot Sock, who's definitely in the top tier, just behind Harrison.