Computer Systems: A Programmer's Perspective: around 2012 / 2013, I went through this book because I took a coursera course based on it. In fact, many universities base their systems courses around this book. It is really well written, has a great choice of topics, and phenomenal exercises [0] for practice (some are legitimately fun).
Operating Systems: Three Easy Pieces: In 2013, I found this book because I was frustrated with the textbook assigned for my operating systems class (Silberchatz). OSTEP has incredibly clear and concise descriptions without skimping on necessary details. It's wonderfully written. I was so jazzed up about this book that I ended up sending a lot of edits / improvements, and the authors gave me a very kind shoutout in the acknowledgements section.
Computer Networking: A Top-Down Approach: In 2013, this was the assigned textbook for my computer networking class. I already owned Tanenbaum & Wetherall which is good, but preferred this book. It is a more approachable treatment of networking (without sacrificing any crucial topics), so better for a first course.
I've heard glowing reviews of The Algorithm Design Manual, Designing Data-Intensive Applications, and Structure and Interpretation of Computer Programs over the years, but I haven't personally gone through them. For the TeachYourselfCS categories that I know the textbook landscape, I find their selections spot-on and pretty refreshing.
