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/
Fermat:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Fermat.html
Hilbert:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Hilbert.html
Mersenne:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Mersenne.html
Wallis:
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Wallis.html