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.

Numerical Analysis

• Numerical Analysis Notes, by Lucio Tavernini
• An Introduction to Multigrid Methods, by Pieter Wesseling
• Numerical Recipes, by William H.Press, Saul A. Teukolsky, William T. Vetterling, Brian P. Flannery
• Templates for the Solution of Linear Systems: Building Blocks for Iterative Methods, by Richard Barrett
• Numerical Analysis at the University of Cambridge
• Lecture Notes on Optimization, by Pravin Varaiya
• Computational geometry, mesh generation, numerical methods, by Jonathan Shewchuk
• Numerical Analysis, by Steven Elliot Pav
• Convex Optimization, by Stephen Boyd and Lieven Vandenberghe

Information Theory

• Information Theory, Inference and Learning Algorithms, by David J.C. MacKay
• A Short Course in Information Theory, eight lectures by David J.C. MacKay
• Primer on Information Theory, by Thomas Schneider
• Several books by G. J. Chaitin (not only Information Theory)

Financial mathematics

• Measure theory, Probability, Stochastic calculus, General theory of processes, Financial mathematics, lectures notes by Rich Bass
• Structural Analysis of Discrete Data and Econometric Applications, editors: Ch. Manski, D. McFadden
• Game theory examples, by Roger McCain (html)

Game Theory

• Gametheory.net, with lectures on the subject
• Determinacy in infinite games, by Jindrich Zapletal

Cryptography

• Handbook of Applied Cryptography, by Alfred J. Menezes , Paul C. van Oorschot, and Scott A. Vanstone
• Foundations of Cryptography
• Lecture Notes on Cryptography
• Cryptography and Network Security
• Cryptography and Cryptanalysis Lecture notes
• Modern Cryptography
• Cryptography and Cryptanalysis, by Glenn Durfee
• Lecture Notes on Cryptography, by S. Goldwasser and M. Bellare

Miscellaneous

• Derivations of Applied Mathematics, by Thaddeus H. Black (GNU Free Documentation License)
• Linear Methods of Applied Mathematics, by Evans Harrell and James Herod.
• Linear Algebra, Infinite Dimensions, and Maple, by James Herod
• generatingfunctionology, by Herbert Wilf
• Algorithms and Complexity, by Herbert S. Wilf
• A=B, by Marko Petkovsek, Herbert Wilf, and Doron Zeilberger
• Applied Math Textbook, by Sean Mauch beta version (unfinished)
• Mathematical Tools for Physics, by James Nearing
• Applied Mathematics, by Peter J. Olver and Chehrzad Shakiban
• Surveys in Combinatorics
• Complexity Theory, by Oded Goldreich
• Papers on Combinatorial Enumeration and Asymptotics, by Andrew Odlyzko
• Hyperplane Arrangements, by Richard Stanley
• Introduction to Statistical Signal Processing, by R.M. Gray and L.D. Davisson