If you are looking for a high-ceiling, high-risk player, consider Trayce Thompson of the Chicago White Sox.
Trayce Thompson, OF, Chicago White Sox
Bats: R Throws: R HT: 6-3 WT: 195 DOB: March 15, 1991
2010: Grade C; 2011: Grade C; 2012: Grade C+
This is my conclusion about Thompson in the 2012 Baseball Prospect Book: Thompson has the highest upside of any hitter in the White Sox system, but he comes from a basketball background and is still figuring out how to use his tools on the diamond.
For 2013, that is Still True. Thompson made some progress in 2012. His strikeout rate remains much too high, and without more adjustments to his swing he has no chance to hit for average at higher levels. However, he's working hard to improve his plate discipline, and while Thompson is never going to win batting titles, if he can hit .250 his other skills will play. He's quite fast and has learned how to steal bases effectively. He's tapped into his natural power and is dangerous if you put a fastball in the wrong place. He's a very good center fielder. I remain quite impressed with his tools, and I think the chance that he'll figure out how to use them is getting better. It isn't a slam dunk, and he needs a full year against Double-A pitching (and probably another year against Triple-A pitching) to fully adapt. That would put him challenging for a regular job in 2015, which seems like a long time from now, but he'll still be just 24. Grade B-, with risk but a plausibly large payout.