Ask HN: Best college course or training you have taken?

Having been to college and taken additional classes and training over the last 10 years myself, what is the best college course or training you have taken and why? Mine: I took an assembly class my first semester of college and I felt like it set me up for a deep understanding of programming and hardware instruction. Also: I took a week long class at the Big Nerd Ranch in about 2001 in Objective-C programming. It was intense, heads down, total focus.