I am relatively new to AfterEffects.
One of the best free (and I would say even for a paid course) is this series of videos I found on YouTube.
It's gotten me up to speed very quickly. And I am sure it would be helpful to others.
The guy, I assume his name is Bucky, has created about 35 tutorials that are easy to follow and non-intimidating.
He covers everything from a basic intro, through mattes, masks, 3D etc.
I ask moderators to make this a sticky.
Youtube and Vimeo are not really worth the effort to mine for good to excellent examples of After Effects tutorials. The search mechanism is terrible because anyone can tag the worst imaginable junk as an AE tutorial and even promote useless clips as worth watching. The hundreds of sample projects and "tutes" requires scrutiny. It is more efficient to use one fo the many AE Tutorial portals instead of attempting to slog through video social sites alone.