Nowadays It is easy to get overwhelmed with all the online classes available ( gumroads, patreons, youtube videos etc. )
Let us use this thread to post our most usefull or recommended classes/courses/tutorials here 
Let me start of by giving a shoutout to āKurt Papsteinā and his tutorial series on Gumroad:
https://gumroad.com/ikameka#
Also, āMike Dafeoā has some very good tutorials and courses out there and has a new one coming up:
http://www.mold3d.com/artists/2015/9/11/michael-defeo