Top books on r/Unity3D

Learning C# Programming with Unity 3D

Introduction to Game Design, Prototyping, and Development

Learning C# by Developing Games with Unity 3D Beginner's Guide

Unity in Action

Head First Design Patterns: A Brain-Friendly Guide

Programming Game AI by Example

Unity 3.x Game Development Essentials

Design Patterns

Clean Code

Pro Unity Game Development with C#

Game Engine Architecture, Second Edition

C# in Depth, 3rd Edition

Unity 5.x Shaders and Effects Cookbook

Code: The Hidden Language of Computer Hardware and Software

Head First C#