Some time ago the Massachusetts Institute of Technology (MIT) has started to release their lectures/courses to the public as so called OpenCourseWare. The idea behind is to open up the world of today's knowledge to everyone.
There are more than 1800 course available online, many of them translated into other languages or even available as audio/video presentations.
The content of the courses touch a huge variety of topics from Architecture and Planning, Engineering, Health Sciences and Technology, Humanities, Arts, and Social Sciences, Management and Science (Biology, Brain and Cognitive Sciences, Chemistry, Earth, Atmospheric, and Planetary Sciences, Mathematics Physics).
The MIT has also just laucnhed a program to deliver special courses for high school pupils.
If you are interested in any of the above mentioned topics it is worth a look !