Nate Silver of BP has an article up on SI.

Markakis clocks in at 34 and Weiters at 32 (and the only Minor Leaguer).

No. 34, Nick Markakis, RF, Orioles, Age 24 (--)

Believe it or not, the Orioles actually placed two young hitters in the Top 50, and another into Honorable Mention. Markakis is probably never going to be a huge power hitter, but with a great line-drive stroke and an even better batting eye, he'll be a top-of-the-order hitter for years to come.

No. 32. Matt Wieters, C, Orioles, Age 22 (--)

Here is the other Oriole -- and the only current minor leaguer to make our Top 50. Since last season, we have significantly revised our minor league forecasts to make them more conservative ... but Wieters still blows the system out of the park, with a 1.038 OPS thus far on the season in spite of playing in some pitcher-friendly environments. Wieters might be in the upper quartile of major league catchers if he put on an Orioles uniform right now -- and he's only 22.

http://sportsillustrated.cnn.com/2008/baseball/mlb/08/21/bp.pecota50/1.html