Courtesy of Edsko de Vries:
Eugenia Cheng and Simon Willerton of the University of Sheffield, a.k.a. The Catsters, have an excellent series of lectures on category theory on YouTube. The only thing missing is some overview of the lectures, which I have provided below. A graphical overview is available too.
I don’t recall ever seeing anyone lecture so excitedly about math. The lectures are not only enjoyable but the enthusiasm is strangely infectious.