When talking about "systems design" people usually refer to books like DDIA, System Design Interview, Patterns of Enterprise Application Architecture, etc. I find these books very theoretical and while interesting, I rarely remember anything and much less I apply what they talk about.

I find the AOSA (The Architecture of Open Source Applications) books much more fun to read, useful, and very hands on. The only "problem" perhaps is that they are not 100% "web" oriented (some chapters are related to distributed systems and the like, but the majority are not).