What classes should I take in high school that would help me in becoming a professional pilot?

Great answer James. I would also like to add that if you have the opportunity, take psychology as an elective. I know that might sound a bit strange, but to stay safe and effective in a multi-crew cockpit (assuming you are choosing to be a career pilot), it helps to understand human behavior. Human Factors (aka CRM) is an important part of flying and tends to be trained to a minimum. Where I am, there are almost 100 different nationalities in the cockpit. The language and cultural barrier can be challenging at times. Luckily, as proven by psychometric testing, it has been discovered that pilots are quite similar despite where they come from.

I looked at Casper's program. I worked as a flight instructor at a similar one with University of Alaska, Anchorage. It was a Part 141 flight school (more organized program) and a very good program. I see that Casper only offers through commercial pilot. I suggest that you continue and get your instructor ratings (CFI, CFII) and teach while you finish your Bachelor's degree. Make sure that you get your 4 year degree!! Best of luck, even though it looks like you won't need much. Keep up the hard work!

From my experience, focus on technically oriented classes but keep yourself well-rounded. I agree that in this day and age, it is wise to take computer classes. Also take as much math class as you can (and still maintain a good GPA). Take physics and "mechanical" type science classes. I think you said you were interested in Foreign Languages, so take those if you can to keep yourself well-rounded. If you have the opportunity, try to take Honors or Advanced Placement classes....anything that gives you some college credit and would lighten the load for what college classes you'd have to take--you'll be grateful for the extra time this will allow you in college...especially if you have to schedule training flights around your academics.

Holly,
Being a pilot covers alot of subjects. Math is a big one as you do weight and balance, conversions and many other things. Science is also a big one. You have to be able to understand weather, the different cloud formations and types and alot more. Yous have to understand aero dynamics, how an engine and all the systems work. When you get into turbines you have to know how a turbine works. The ignitors, a hot start, compressor. It really sounds like alot, but as a student pilot you learn this and you will have to know it as an instructor. Go to an aviation college to get your degree and your ratings.

All the other answers here are excellent, not sure that I could add a lot more here. I was not aware that you can select different courses in High School, other than French or Spanish.
To become a pilot, you really just need flying lessons, a lot of them! All the other training will make you a better human and more efficient, which will open a lot of other doors later in life. You can't go wrong with education, the more you know, the better off you will be. "Knowledge is power"
I agree with Sean, as a pilot, you are the front line person that the customers sees, psychology will help you deal with people better and make you a better communicator. Flight training will give you the technical knowledge, but you still need the soft skills.