William Jennings Buckner has long been a favorite of mine dating back to his days at the University of South Carolina where in 2004 he struck out 105 batters with 23 walks in 84 innings of work.
Buckner's main weapon is a knuckle-curve, which he compliments with a fastball that sits mostly in the low 90's. He gets good sink on the fastball and his groundball/flyball numbers are consistently above 2/1. In that respect, it's also a good sign that even when he was pitching at High Desert in 2005 and 2006 he still allowed only 16 home runs in 165 innings.
Obviously his biggest issue is with walks. If he can cut back on those he stands a good chance of being a middle or back of the rotation workhorse. Given his strikeout rate and ground ball tendencies, he can probably get away with pitching to contact when he starts getting deep into the count. Just give them the sinking fastball and stop trying to be fascist.
The Royals have a number of prospects who are this same kind of midrange prospect. Tyler Lumsden and Danny Christensen fit the profile as well. Their ceilings are as #3/4 starters. If Buckner doesn't improve on his control, he could feasibly be a long reliever.