Pretty broad question. Depends if you want a park ski or an all/big mtn ski. Not many park skis are stiff. Some on the stiffer end are Nordica Ace of Spades, Armada Pipe cleaner, and JO's.
There are plenty of big mtn skis that are stiff, but many are not really made for skiing switch, they just have a twin for billy goating and making it easier to turn. e.g. Moment Belafonte/Garbones, ON3P Wren, Line mothership