Alexandre Stefanov long maintained a list of
online math texts and other materials at Geocities, but it appears
that his original web site is no longer available.
Because these resources may be of interest to our readers,
we present here a modified version of Stefanov's list as of November 18, 2009.
We welcome corrections or suggested additions to this list.
See also Math on the Web, compiled by the American Mathematical Society, for more online math resources.
Note added August 31, 2010: I just went through and cleaned up the links on these pages; 54 online resources have disappeared
since I started these pages, including 18 books that were previously distributed online by the American Mathematical
Society. It appears that with improvements in Printing-on-Demand (POD) technology, people are no longer
putting out-of-print books on the web, they're trying to make some money selling a few books a year instead
of distributing thousands of free copies online.
People can do both; see, for example, Convex Optimization by Stephen P. Boyd and Lieven Vandenberghe, a great book that's available online while Cambridge University Press publishes a hardcover version for people who want one.
These online resources are still important.