Selected Papers on Geometric Algebra in Quantum Mechanics  
   These papers analyze the quantum mechanical Dirac theory of the electron with respect to its geometric structure as revealed by reformulation in terms of Spacetime Algebra
   http://modelingnts.la.asu.edu/html/GAinQM.html

The Quantum Theory of Particles  
   A new approach to relativity, quantum mechanics, and field theory which solves many old puzzles, such as ultraviolet infinities and superluminal spreading of wave packets.
   http://www.geocities.com/meopemuk

An Introduction to the Lorentz-Dirac Equation  
   Notes by Eric Poisson providing two derivations of the Lorentz--Dirac equation.
   http://arxiv.org/abs/gr-qc/9912045

Relativistic quantum mechanics  
   An electronic textbook for relativistic quantum mechanics is presented. It can be ordered free
   http://rel.qm.walterpfeifer.ch

The Klein-Gordon Field  
   A brief overview of the lagrangian for a Klein-Gordon field, by Professor John Norbury.
   http://fisicanet.terra.com.br/unificacao/quantum-field-theory-by-john-norbury.pdf