Ok so to answer this question I browsed through BBHQ's minor league equivalent statistics, first looking for players with extraordinarily high PX and SX, then looked at milb equivalent stats. A few players I pulled out that are curently in majors, or competing for a job include: Matt Kemp, Ryan Braun, Corey Hart, Hunter Pence, Felix Pie, Justin Upton, Joey Voto, and Chris B. Young. The only players I found that qualified not in the big leagues were Brandon Jones and Brandon Wood. Cameron Maybin was not in those milb equivalents but he is top on my list of potential 30/30 guys in the minors. So heres the list.
1. Chris B. Young (fastest bat speed in league, Bary Bonds without the batting eye, as close to 40/40 guarantee as possible)
2. Corey Hart (30/30 written all over him)
3. Matt Kemp (same as Hart)
4. Ryan Braun (could steal 30 bases but wont do it consistently)
5. Felix Pie (great upside but power might not develop as planed)
6. Justin Upton (he might be best player in baseball by 2015, better than BJ)
7. Cameron Maybin (40/40 upside here)
I took Pence, Voto, Jones, and Wood out of the list because I don't think they quite meat one of the qualifications for 30/30 (although statistically they fit my MiLB equivalent numbers.) Chris B. Young, Justin Upton, and Cameron Maybin are the highest potentials on the list and have 40/40 potential.