I've been trying to continue to learn about computer science and software in general through free online classes, but a lot of them are just taught by really dull professors. Which open courseware class have you found to be the most interesting and informative for a software engineer?
Note there is a list of colleges offering free online courses here. (If you have a better list of free online courses feel free to edit the question.)
Matrix Algebra - MIT. Unusual maybe, but you're just asking for preference, so there's mine.
My personal favorite is Introduction to Algorithms.
I have been watching the lectures and studying the textbook as a personal project, and it's been a pleasure.
Pro #1: One of the professors is Charles Leiserson, aka the L in CLRS, one of the most well-regarded algorithms textbooks.
Pro #2: Erik Demaine, the other professor, is a great lecturer and a joy to learn from.
Pro #3: Algorithms are FUN, especially when taught correctly.
Pro #4: A lot of the supplementary information is provided, including solutions to assignments, and full transcriptions of lectures. This is lacking in many OCW courses.
I found another great library of lectures at http://www.academicearth.org/subjects/computer-science. My favorite has to be the class on robotics (although it can get a bit too complicated at times).