This is one of the best all around sites that I have
found. It is titled "The MacTutor History of Mathematics
Archive."
http://www-history.mcs.st-and.ac.uk/~history/
This is an award-winning site that links
to all sorts of mathematics information.
http://archives.math.utk.edu/
Gauss:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Gauss.html
Jordan:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Jordan.html
This site, entitled "Matrices and Determinants,"
is listed here under the history subsection because of
its excellent review of the history of solving systems
of equations using matrices.
http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Matrices_and_determinants.html
