6.01 Intro to EECS I: This introductory class is based around writing Python code and building circuits for programmable robots. It covers a potpourri of topics from object oriented programming to Bayesian updates, but none in depth. The class also has standards: if you're not careful, you just might get a lower-than-expected grade.
6.828 Operating Systems: This rigorous semi-lab class is awesome for one (and only one) reason: building your very own operating system! I was not a fan of using a toy operating system to teach operating system concepts since I had very little background prior to taking the class, but the case studies covered in the second half of the class were cool. This class easily becomes a time sink: a small bug from a previous lab can add another ten hours of debugging to your time spent on the current lab.
15.279 Managerial Communication: This class teaches strategic communication using a variety of contrived exercises. Sadly, this class does discourages an appreciation for thoroughly researching and knowing subjects of importance.
15.437 Options and Futures: This class covers futures, options, and credit derivatives. The first two topics were hot, the last one was not. I also wish this class went more into modeling, but that's what 15.450 is for.
18.440 Probability and Random Variables: This class is basically Art of Problem Solving Intermediate Probability and Combinatorics. And random variables.