I recommend not just any chemistry course but specifically this one:
MITx 3.091 "Introduction to Solid State Chemistry"
It's "archived" - good enough, everything is accessible, you just won't be able to get a "grade".
It's the gateway to "materials science" too. It is more at the edge of chemistry, towards physics and engineering. Not to mention that the teaching in this course is pretty good. Also, it is not dumbed down, you can go to MIT, take the same course and feel right at home. It's about properties of materials as a consequence of the chemical/physical properties of the components (atoms/molecules) and how they are structured (example: diamond and graphite are both made of carbon, then why are they so different).
If you want to get up to speed on "just chemistry" try Khan Academy, their explanations are pretty good and you can easily select what interests you because it is broken down into many small pieces.
• MITx "Introduction to Solid State Chemistry" . I've never been good at chemistry, but this course managed to make it clear to me.
• MITx "Circuits and Electronics"  (three links because they have split it into three courses since I took it). Most electronics courses have not worked well for me. Some fail by using analogies that don't work for me. The analogies are either to things I don't understand, or to things I understand too well compared to the target audience for the course.
The latter might seem odd--how can understanding the analogous system too well cause a problem? It's because there usually isn't a perfect match between behavior of the analogous system and electronics. The more you know about the analogous system, the more likely you are to know about those places that don't match. If the author expects the students will not know about those parts, they won't mention the limitations from those parts. So you can end up expecting too much of the analogous system to apply.
Other courses have not worked for me by being too deep and detailed. For instance at one time I knew, from a solid state physics intro I took, how a semiconductor diode worked at a quantum mechanical level. I could do the math...but the course gave me no intuition for actually using the diode in a useful circuit.
The "Circuits and Electronics" course struck for me a perfect balance.
• MITx "Computation Structures" . At the end of this three part course (of which I only took the first two parts), you will know how digital logic circuits work at the transistor level, and you will know how to design combinatorial and sequential logic systems at the gate level, and you will know how to design a 32-bit RISC processor...and you will have done all those designs, using transistor level and gate level simulators.
As I said, I only took the first two parts (didn't have time for the third). In the first two parts we did cover caching and pipelining, but we didn't use them in our processor. I believe that in the third part those and other optimization are added to the processor.
• Caltech "Learning From Data" . The big selling point of this course is that it is almost the same as what Caltech students get when they take it on campus. The only watering down when I took it was the homework was multiple choice so it could be graded automatically.
The most outstanding thing about this course was Professor Abu-Mostafa's participation in the forums. He was very active answering questions. I don't know if he still does that now that the course is running in self-paced mode.