1. Pragmatic Programmer Many pearls of wisdom about the development process 2. The C Programming Language Established the foundation for my early career 3. The Mythical Man-Month Gave names to problems I'd experienced in my career. 4. Accelerate Taught me the metrics and means of improving the software delivery process 5. Refactoring Defined and named patterns for improving a codebase There are others that could fit into a top 5 depending on what I'm working on at the time, (Gang of Four, Programming Pearls to name a couple).