The Jack London Collection:
http://sunsite.berkeley.edu/London
Huge site with helpful links to information about London.
Jack London International:
http://www.jack-london.org/main_e.htm
Another major site with extensive information and links on London.
E-text
http://sunsite.berkeley.edu/London/Writings/LostFace/fire.html
of "To Build a Fire" along with a concordance (a tool to find specific words in context).
FBI file on London
http://foia.fbi.gov/london/london1.pdf
(Adobe Acrobat format).
The Jack London Society:
http://sunsite.berkeley.edu/London/Organizations/jl_society.html
Sponsors a biennial Jack London conference.