While those players are certainly dominant when it comes to the premier off-speed pitch, the mantle of the most unhittable pitch in 2006 goes to the slider of Fernando Cabrera.
Cleveland's young reliever recorded a Whiff Rate of .652 on that breaking ball, and, if you think that's a fluke, think again. Had Cabrera qualified the year before, 2006 would have been the second consecutive season his slider led the league. In 2005, Cabrera posted an eye-popping Whiff Rate of .762, though in limited action (42 swings).
Interestingly, Cabrera only threw his slider in the strike zone 28.6 percent of the time, well below the major league average of 41.6 percent. In other words, he makes the pitch unhittable with a late bite that places the ball outside the plate or in the dirt much of the time.