Clifford Algebra to Geometric Calculus: A Unified Language for Mathematics and
Physics (Fundamental Theories of Physics). This book is intended for mathematicians
and physicists rather than programmers, it is very theoretical. It covers the
algebra and calculus of multivectors of any dimension and is not specific to 3D modelling.
Visual Complex Analysis - If you already know the basics of complex numbers but want to get an in depth understanding using an geometric and intuitive approach then this is a very good book. The book explains how to represent complex transformations such as the Möbius transformations. It also shows how complex functions can be differentiated and integrated.
Geometric Algebra for Physicists - This is intended for physicists so it soon gets onto relativity, spacetime, electrodynamcs, quantum theory, etc. However the introduction to Geometric Algebra and classical mechanics is reasonable.
Geometric Algebra for Computer Science: An Object-oriented Approach to Geometry. This book stresses the Geometry in Geometric Algebra, although it is still very mathematically orientated. Programmers using this book will need to have a lot of mathematical knowledge. Its good to have a Geometric Algebra book aimed at computer scientists rather than physicists. There is more information about this book here.
Roger Penrose - The Road to Reality: Partly a 'popular science' book as it tries to minimise the number of equations but it still has lots of interesting results that its difficult to find elsewhere.
