I personally took my first steps in learning solidity with Bitdegree. They have this interactive and gamified solidity course for beginners. I saw that they also have an intermediate level solidity course but I didn't catch the time to try it yet. Here is the link:
I also agree with AfriDylan about Hackr.io site, I recently found it and it seems to be a very good source for finding various programming courses. How they work is that anyone can submit a course but at least 66% of moderators need to confirm it in order to include the course on the website. And they have some listing rules which prevents listing crapy content. So I think this is a trustable source.