Nash-equilibrium.com
Very interesting site by Michal Baye, John Morgan and Patrick Sholten that debunks the myth
that on the Internet only low-price firms survive. Lots of good information on
the industrial organization of the new economy.
William Trochim's Research Methods Knowledge Base
Contains an excellent introduction to the idea of statistical power and also a link
to the even more excellent 'OJ' Page
which illustrates by the way of the OJ Simpson trial significance level, statistical power, and errors type I and II.