Here are a few more ideas to try in your next circuit routine. Balance is the theme this time, and improved balance can certainly help with ski technique.
1. Clams in a side plank.
Lots of skiers and runners can benefit from doing the clam exercise, since poor glute activation is common. By doing the clam with an elevated hip, it adds a balance challenge. It also forces you to keep your hips straight up, otherwise you will probably fall over. Be sure to engage your glutes to lift your bent leg.
2. Side plank, bringing extended leg forward.
Again, this is a good core/balance exercise. Keep your core tight, and try not to let your hips drop. Also try to avoid shrugging at your shoulders. Bring your top leg forward to a 90 degree angle from your torso.
3. Airplanes with a calf raise.
You may have tried walking airplanes before as a balance exercise. Aim for a flat back and lift your leg to the point of being horizontal. You can add a challenge by doing a calf raise in the 'airplane' position. This one is tricky.
Balance drills on skis or roller-skis are also a great idea, since balancing while moving tends to be more difficult. Sheila provides some great ideas for doing that here: http://www.xcottawa.ca/articles.php?id=1033