MIT OpenCourseWare - Free to all

MIT OpenCourseWare makes the materials used in the majority of MIT's undergraduate and graduate courses—more than 2,100 in all—available on the Web, free of charge, to any user in the world. OCW receives an average of 1.75 million web site visits per month from more than 215 countries and territories worldwide. To date, more than 125 million individuals have accessed OCW materials. MIT OpenCourseWare is supported by donations from site visitors, grants and corporate sponsorship including our Next Decade Alliance sponsors Ab Initio Software Corporation, Lockheed Martin, MathWorks and Dow Chemical.

http://ocw.mit.edu/index.htm The list of courses is here

http://ocw.mit.edu/courses/index.htm Something every one should know and use.