Coxeter Matroids: Neil White's research papers (mainly PS).
Coxeter Matroids: Alexandre Borovik's introductory notes, examples and research.
Matroid: Introductory article from MathWorld with links and references.
Matroid Decomposition: Electronic library of mathematics monograph by Klaus Truemper.
Matroid Miscellany: References, sources and open problem, collected by Thomas Zaslavsky.