a list of more than 200 MOOCs and free certificate programs.
Stephen Downes also has a nice MOOC listing going on his MOOC.ca page.
Applications for Education
Some MOOCs, like this biology course through Harvard and MIT's EDX program, can provide a good challenge to high school students who have the interest and initiative to complete it. I'm not aware of any high schools that are doing this yet, but it seems like it's only a matter of time before some high schools start awarding some type of recognition or credit to students who earn a certificate of completion from a course through EDX and similar programs.