Udacity offers free computer science related courses. They offers certificates of completion for these courses as well. However I have avoided mentioning websites like this, as compared to established universities who have been doing the same thing because, well... Stanford and Princeton are a lot more prestigious than some website nobody has ever heard of.
However Udacity founder Sebastian Thrun plans to change that. In this interview he mentions that he is looking to pair up with testing centers so that students can receive a more valid form of certification in the classes they take. While the classes will remain free, the certification is what would cost money.
This situation offers an interesting question. Can websites receive certification? If University of Phoenix can be run as a for profit school, and Liberty University can give away science degrees with full accreditation while teaching creation science, why not Udacity? This could be a tremendous slap in the face to all the private and public colleges and universities in the US that have gradually been increasing tuition every year. This can't happen soon enough.