Good luck with finding waterski specific training on the web. I would look into cross-fit workouts. I tend to focus on pushing exercises in the summer and pulling exercises in the winter. The reason for this is that during the summer months, you are doing a lot of pulling style work while skiing. You the pushing exercises to balance you out. During the winter months, for on a slightly heavier pull vs push workout. I work with a trainer and strongly recommend it. They can teach you proper technique so that you don't get hurt.
Study the principles of HIIT (Hight Intensity Interval Training) training. The key words here are High intensity and Interval. Some machine work is good. But, free wgt's if done properly do a much better job of Balancing out your muscles, (rt. side vs. lt. side, etc...) while developing general balance and stability.
I would suggest looking into any kind of training that you will enjoy, that will challege you and that is personally rewarding...
Look at routines for football players, Boxing, MMA, UFC and Mountain biking. These will give you some great idea's to add to a progressive w/o plan that keeps changing slightly every 3 wks. These will also give you Strength, explosive strength, core strength, agility, flexability, cardio and skeletal Balance...
Good Luck! -old man winter is just around the corner...
Speaking of HIIT, I found this site not too long ago: www.bodyrock.tv/
I thought the workouts would be great conditioning for slaloming. I bought a timer and started to do some interval stuff and the workouts seem to fly by (Note: Gymboss has a free timer app in the app store which I later found out).
Also, with this particular website, you may find that it's not that hard to watch the demonstrations either.