Law. Don't remember the exact name of the class, but it was taught by a real hardcore New York lawyer. He was tough on us, I didn't do so well, but I learned a lot about the real legal system, not some theoretical idealization of it.
Math in diverse cultures *
Theater
Biology 1 + 2
Spanish 1 + 2
Sociology *
Psychology *
As a comp-sci student, these electives really got me interested in a lot of cool stuff.
I hate to say this but... none. At George Mason University we were required to take a lot of electives, and many classes for no credit that only added to the cost of our education. They did keep employed numerous GTA's, however.
A math elective called 'quality control and reliability'. Sounded super boring but I absolutely loved it. It was fascinating to see math in a business-y useful context.