In no particular order, here's the list of my favorite places to study new things.
DevU - used to be LearnVisualStudio.net - courses that covered everything .Net, VisualStudio, C#, Microsoft Tools. I got a lifetime membership. One of the best purchases I made in my junior years.
Pluralsight - Love it! Excellent IT, DevOps, Management, and other topics!
EDX - Free Online University. I love their Micro Masters and Certifications.
There're others, of course, but the above three are my favorite ones.
Highscalability.com is not a site where you find courses, but I love it for its "Stuff that Internet says on Scalability..." that are posted every Friday. If you're into high traffic, big data, fast and edge technologies, I strongly recommend this site. Even if you aren't it's still going to be useful to you :)
What are your favorites sites to learn and sharpen your skills?
(open source and trusted by devs everywhere ❤️)