I'm a college professor who teaches the courses in the border between math and computing. Lots of good suggestions here about subjects. I have a methodology suggestion. Try to do active learning as much as you can. (You can look at the MAA's recent book for a good state of the art summary.)
Yes, ivan_ah is right, that's the book I meant. Free and evidence-based. I'd say active learning is baked into pretty much all the chapters of the book, because the evidence is very strong that this is the best way to go.
