What courses should I take in high school if I want to be a forensic scientist?

If your school has a Forensic Science class, then that would be an obvious choice. My school did, and that's what I took in my senior year. It was a fascinating subject. Otherwise, it doesn't matter. Your high school classes are really only preparing you for your future college classes. Your degree will prepare you for the actual career in forensics. In college, it would be wise to take a lot of Biology, Chemistry, and Physical Anthropology classes, especially classes like Forensic Anthropology. Psychology wouldn't hurt either. Stuff like that.

Edit: If your school does not have a Forensic Science class, then the next best thing is probably Human Anatomy. That is also pretty important to know.