The Lockheed P-38 Lightning had counter-rotating props as well. As in the Seneca/Seminole/Chieftain the props were laid out so that the left one rotated clockwise and the right one rotated anti-clockwise (when viewed from behind). All the benefits of a lower Vmca, no critical engine, etc.
Trouble was, the props produced an unacceptable down-wash on the rather large tailplane at high power settings so they swapped the rotation. Now they had an up-wash at high power settings (which apparently was OK) but also a higher Vmca. As far as I know this was the only time that this arrangement was tried on a production aircraft. Anyone else have any more info?