Interesting topic. The best HS athletes I have ever seen in person may not qualify as pure athletes, like a Tim Dwight who excelled in multiple sports.
Close to all of the best 'athletes' I've ever seen play have been basketball players
Raef LeFrentz...I watched that guy dunk so hard, over and over and over, in the stste tournament, he knocked a bolt loose from the backboard. Plus, the guy could stroke it when he needed too.
Ricky Davis...quite possibly the most insane vertical leap I've ever seen...in person, and again at the state tournament. That kid could fly.
Nick Collison...nobody dominated like him. He absolutely embarrassed entire teams by himself...so much so, he was depants during the opening tip in a high school game. That was the only thing the other school could do to win...at something.
Adam Haluska...very good all around BB player, and FAST (track star as others have mentioned). He was a pretty good leaper, too.
Harrison Barnes...probably don't need very much explanation here.
On the "who the **** is that" list, I have a couple from the Des Moines Metro.
Glenn Phillips (DSM North)...best BB player who never went on to do anything with himself I have seen in my life. He was just as good, or better, than Ricky Davis. Too bad he went to North (OUCH).
Jermaine Reed (DSM East)...finally out of my BB fixation. The best RB this great state of Iowa has ever seen. Had offers from the likes of Bobby Bowden/Florida State, Lou Holtz/Notre Dame and Joe Paterno/Penn State in the early 90's. Could not qualify (sad).