Brett Terpstra and Ryan Irelan are two of my favorite people on the internet, and when I found out they came together to make a course on OS X Shell Tricks on Mijingo.com, I couldn't resist. I got a lot out of this course considering that I was pretty weak on Shell commands coming into it. The section on files and directories alone was worth it to me.
As someone who makes a lot of educational video myself, I have a lot of respect for the quality of Mijingo's products. Another thing I'm realizing more and more: When it comes to any form of online education, I usually can't afford the time cost of "free." Give me a reasonably priced video course with high production values over wasted hours of YouTube searching any day.