After taking Gamedev.tv's C# design patterns course I moved on to their Unity UI Toolkit course. It was fun, and made me look at some aspects of programming in a new light. I also learned how to use a whole new system in Unity, as well as the underlying concepts of XML and CSS. I learned to build my own custom editor Unity UI.
I used the knowledge I had gained from this course to create my own simple task manager, which you can find on the Unity Asset store here.