Twister S.A. Walls Barrel Stirrup
The Twister is just as its name implies. The stirrup is twisted. The inside arm is tilted toward the head of the horse, and the outside longer arm is tilted toward the rear of the horse. This helps give you that "turned fender" feel. It also has the slanting concept that puts your foot parallel with the ground. This really helps take the torque out of your knees and ankles, and allows for the natural alignment of your hips and legs.
Also, if you lose this stirrup, it makes it easier to find.