Murad Campbell (Overbrook HS). Dude coasts through a 4:30 mile at the Meet of Champions, looks up at the crowd and smiles in a showboat way, and then continues on to run something like 8:57 with no competition. Reason for demise? Heard he went to a community college out west, that's all I know.
Matt Elmuccio. Steve Slattery's competition in NJ. Both went to Colorado. Elmuccio wound up injured and burned out with their high mileage, but Slattery wound up a star.
Fred Sharpe. Triples in the 400IH, 800m, and 1500 (I think he was something like 2nd or 3rd in the 1500m, but won the other two.) I saw his name in college once or twice, but not much after.
Lastly, since this IS Letsrun.com, Alan Webb. Sets a national high school record, the first high school kid in ages to go sub-4, and the guy can't even break a world record. By LetsRun standards, he has done nothing.