Towers of Hanoi problems are good examples in that they are easy to visualize, and their relationship to sorting with stacks is obvious.

However, if you are selecting problems for a syllabus, please be aware that "easy to visualize" can actually give an unfair disadvantage to some of your students. I've commented on my own affliction with regard to using GUIs and learning to program.

I completely understand the algorithm for Towers of Hanoi, and why it works, and have translated it into a few languages. But I understood it only by playing with physical disks or marks (and erasing) on a piece of paper. I could never have constructed it by "visualization", since my brain doesn't work that way.

So, beware when you pretend you know what skills are "universal" about thinking... you may have wrong thinking about that. {grin}