The books recommended here range, in my estimation, from excellent to genius: enjoy!

Agile: Getting Started
Beck & Andres, Extreme Programming Explained
Benson & DeMaria Barry, Personal Kanban
Cohn, User Stories Applied
Schwaber & Beedle, Software Development with Scrum

Agile: Technical
Beck, Test-Driven Development
Feathers, Working Effectively with Legacy Code

Agile: Additional, veering into Deming, Lean, the Theory of Constraints, and Real Options
Anderson, Kanban
Benson, Why Plans Fail
Benson, Why Limit WIP
Derby & Larsen, Agile Retrospectives
Goldratt, The Goal
Goldratt, It's Not Luck
Johnson & Broms, Profit Beyond Measure
Liker, The Toyota Way
McCarthy & McCarthy: Software for your Head
Ohno, Taiichi Ohno's Workplace Management
Maassen, Matts & Geary, Commitment
Reinertsen, The Principles of Product Development Flow
Rother, Toyota Kata
Scholtes, The Leader's Handbook

Argyris, Overcoming Organizational Defenses
Bernstein, Emotional Vampires at Work
de Bono, Six Thinking Hats
Dweck, Mindset
Elgin, How to Disagree Without Being Disagreeable
Galwey, The Inner Game of Tennis
Galwey, The Inner Game of Work
Stolovich & Keeps, Training Ain't Telling

Goldberg, Writing Down the Bones
Johnstone, Impro

Alexander, The Timeless Way of Building
Brooks, The Design of Design
Cooper, The Inmates are Running the Asylum
Ruskin, The Humane Interface
Schell, The Art of Game Design

Functional Programming
Friedman & Felliasen, The Little Schemer
Abelson and Sussman, Structure and Interpretation of Computer Programs

Allen, Getting Things Done

Project Management
Brooks, The Mythical Man Month
Thomsett, Radical Project Management
Rothman, Manage It!

Start-ups & Entrepeneurship
Blank, Four Steps to the Epiphany
Cooper & Vlaskovits, The Lean Entrepeneur
Moore, Crossing the Chasm
Semler, Maverick!