I did the MIT 6.00.1x, which is very recommendable, since I still learned a bit, even having a CS degree. Especially since I wanted an easy entry into Python programming. I peeked into several others which were not that interesting (to me!) and also time-consuming. Currently I watched a couple of weeks of "UT.9.01x Effective Thinking Through Mathematics", which is sadly taking another course than I expected, I don't know yet if I'll stick to it. Last week "Think101x The Science of Everyday Thinking" started which already looks really interesting. Here is an overview of the course. Not time-consuming, interesting, great guest speakers and thought-provoking. I will very likely stick to that. A couple of other ones I marked to check out for me is "GSE1x Unlocking the Immunity to Change: A New Approach to Personal Improvement" and "ANU-ASTRO1x Greatest Unsolved Mysteries of the Universe". And I haven't really been browsing edx' catalogue lately, which increased by a lot, otherwise I'd have more on the list. Depending on how much time you want to invest, you can probably spent a 40 hour week on edx easily.

What I like about edx, too, is the fact that I wouldn't be ashamed on putting the certificate to my CV / an application. Even the free ones offer at least a PDF with your name and the name of the course and a link to check if the certificate is valid. While this does not prove that you didn't cheat your way through the course, I highly doubt that this concern outweighs the knowledge, commitment, dedication and your personal interest into growing in an application interview scenario. There is absolutely nothing to lose and I felt it added a lot to my personal knowledge and in case I'll have another job interview, it's a super easy topic starter which reflects a lot of good characteristics.