Emeka would have to be the big one - I don't think anyone could have seen that coming.
Hilton and Adrien having NBA careers certainly didn't seem likely coming out of high school. Kemba becoming Superman as a junior was a surprise. Back in those pre-internet days, the only time we saw Rip was when he was getting stuffed by the rim in the McD's game, so his career was probably better than we thought.
Honestly, the fact that so many guys can be seen as overachieving is probably (definitely) a credit to JC. He musta had something to do with all that.