Academic Earth is a great collection of free courses and lectures from a variety of schools and websites. Courses can be searched by subject, university, or instructor. Subjects include Astronomy, Biology, Business, Chemistry, Education, Engineering, Law, Math, Physics, Psychology and much more. Universities include Berkeley, Columbia, Harvard, MIT, NYU, Princeton, Yale and more. This is a good resource for teen to find courses, brushing up on material, or as a supplemental homeschool resource.