Advanced and Helpful Programming Online Courses (Paid or Even Free?)

Is there a good website with paid (subscription or per course) model where you can really learn advances programming skills? Are they worth the money?

I found some examples:

* Pluralsight * SitePoint * Udemy

What about free alternatives? Are they (more) useful?

Maybe?

* MIT Open CoursWare

Or any other?

Are you using such?

Do you have such subscription, maybe provided by your employer?