http://www.class-central.com/
provides a complete list of free online courses offered by Stanford's Coursera, MIT and Harvard led edX (MITx + Harvardx + BerkeleyX), and Udacity
Course counts by category:
Category NN %%
Computer Science 81 38%
Healthcare, Medicine, and Biology 29 14%
Physical & Earth Sciences 16 7%
Humanities and Social Sciences 16 7%
Economics & Finance 13 6%
Mathematics and Statistics 10 5%
Statistics, Data Analysis, and Scientific Computing 9 4%
Entrepreneurship 9 4%
Society, Networks and Information 8 4%
Electrical and Materials Engineering 7 3%
Business & Management 5 2%
Education 4 2%
Complex Systems 3 1%
Chemistry 1 0%
Civil Engineering 1 0%
Physics 1 0%
Design 1 0%