ESPN.com's Keith Law listed his sleeper prospects for each MLB organization. Here's who he chose for the Rangers:
Right-hander Cody Buckel had a tremendous pro debut in 2011, showing the ability to mix four pitches, led by an average fastball and a curveball with tight rotation. He has a lean frame, but is athletic with good body control. I also like Colombian catcher Jorge Alfaro's tools -- hit, power, catch and throw -- but he has no plan at the plate right now, as shown by his 54 strikeouts and three unintentional walks in 171 plate appearances last year, making his .300/.345/.481 line rather amazing in context.
You can read the whole list here and navigate to his overall rankings and top-100 list (insider).