Learner.org offers many online classes programs and lectures suitable for high-school homeschoolers. I've enjoyed The Art of the Western World. This is a PBS style documentary with vivid detail that is a joy to watch. The program is not produced from a biblical viewpoint so parents should watch it with their children and discuss the various interpretations offered by the program.
Another great help to parents is learner.org's The Mechanical Universe. This complete introduction to high-school and college physics will interest student and parent alike. It's not a rigorous classroom lecture, but another PBS style documentary. Just enough math is provided to motivate the student to dig deeper and interact with the concepts and equations found in traditional "textbook" physics. Study Notes and coordinated textbooks are available for purchase on the site. We haven't seen these personally. I have not watched the entire series yet and would advise Christian parents to watch with their kids and discuss any materialistic assumptions presented.
Take advantage of these Arts and Science programs, as well as the dozens of others offered at learner.org.