Sites

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

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

Selected Papers on Geometric Algebra in Quantum Mechanics (Popularity: )
http://modelingnts.la.asu.edu/html/GAinQM.html
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