I am a bit of a bookworm. These are the ones that affected me the most.
Software Development
“Test Driven Development: By Example” by Kent Beck
“Growing Object-Oriented Software, Guided by Tests” by Steve Freeman and Nat Pryce
Consulting and Management
“Cynefin - Weaving Sense-Making into the Fabric of Our World” by Dave Snowden, et al.
“Team Topologies: Organizing Business and Technology Teams for Fast Flow” by Matthew Skelton.
“Coaching Habit: Say Less, Ask More & Change the Way You Lead Forever” by Bungay Stanier Michael.
“Crucial Conversations: Tools for Talking When Stakes Are High” by Kerry Patterson , Joseph Grenny , et al.
“Difficult Conversations: How to Discuss What Matters Most” by Douglas Stone , Bruce Patton, et al.