Select Courses, a service designed to help people find online degree programs, has posted a list of 100 free courses covering a wide range of topics. The complete title of their list is 100 Awesome Open Courses for Those Who Want to Change the World. The list is divided into nine sections spanning topics from health to environmental science to engineering, politics, religion, and education.

Applications for Education
All of the courses in the list are designed for college students, but many of them could be used by high school students for independent study and supplements to their high school courses.

Here are some related resources that may be of interest to you:
MIT Open Courseware
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