Coursera will be offering 100 online courses and they are all free! Courses from Princeton, Caltech, Stanford, Duke, Johns Hopkins and more will be offered across 16 categories. Perfect for high school students wanting to dip their toes into the college lecture experience or for pursuing their interests.

How Coursera Works
Universities submit scheduled lectures for mass viewing online. Courses can be anywhere from 4-10 weeks in length. They understand you may be busy during the week and need to watch it at 1am when everyone else is asleep and that is fine, just as long as you watch the lecture weekly. There are quizzes and if you wish to receive a certificate of completion, a final is available (for most courses). It is a new system, so they are working some things out as they go. For the complete pedagogy, click here.   

For more information check out this article from The Atlantic: The Single Most Important Experiment in Higher Education

Update:
9/19/12
Coursera added 2 more categories, 17 more universities and 100 more 'massive open online classes' (MOOC) to it's already growing platform. For a total of 18 categories, 33 universities and over 200 MOOCs.

Education Site Expands Slate of Universities and Courses