Matroids

Coxeter Matroids
Neil White's research papers (mainly PS).
http://www.math.ufl.edu/~white/cox.html

Matroid
Introductory article from MathWorld with links and references.
http://mathworld.wolfram.com/Matroid.html

Matroid Decomposition
Electronic library of mathematics monograph by Klaus Truemper.
http://www.emis.de/monographs/md/

Matroid Miscellany
References, sources and open problem, collected by Thomas Zaslavsky.
http://www.math.binghamton.edu/zaslav/Matroids/