It depends on the course - you're asking questions now that you could find the answer to by looking on the websites of the specific courses. Yes I think something like the CS50 course, SEE courses and maybe a udacity nanodegree would be a good start, that is why I suggested them. As for how employers will look at them, that will vary - some employers clearly value udacity nanodegrees for example, if you look on the website you'll see some of the modules are created by employers. Likewise there are employers creating industry related courses on EDX too. Other employers might not have even heard of them.
These aren't generally considered to be the equivalent of formal education though, I wouldn't want to give that impression, but they're at least a way of demonstrating that you've studied something (especially if you've got coursework, projects etc.. to show for it). So even if an employer isn't familiar with MOOCs being able to explain what you've learned or being able to show what you've created could be useful regardless.
