A Low Level Curriculum for C and C++
is something I wish I add when I learnt programming (there are several articles in that series) because it answered a lot of question I had about how things actually works and allowed me to dig deeper (even though I'm still a novice at those sort of things).
The black board episodes of handmade hero are also a good source of knowledge. The episodes when Casey explained how the CPU and systems work (instruction pipeline, caches, address translations, virtual memory...) were also things I would have loved to know earlier.
Those are things that I wouldn't have known existed (or though were out of reach) and matter if someone didn't pointed them to me.