Please add links to other resources that you are aware of.

**Encyclopedic resources:**
On-Line Encyclopedia of Integer Sequences |
PlanetMath.org |
Eric Weisstein's World of Mathematics |
Wikipedia

**Other online resources:**

- arXiv.org e-Print archive
- Citeseer: Scientific Literature Digital Library
- Keith Kearnes, General Algebra and Lattice Theory Conferences, contact researcher, mailing list, bibliography,...
- MacTutor History of Mathematics archive Biographies of mathematicians, index of famous curves, ...
- MathSciNet Mathematical reviews (requires subscription)
- RelMiCS: Relational Methods in Computer Science Conferences, tools, mailing list, bibliography,...
- WikiBooks Free open content textbooks and other classroom texts
- Zentralblatt MATH Reviews of mathematical papers (free queries for $\le 3$ reviews)

**Books and surveys available online (see also http://www.ams.org/online_bks/online-books-web.html):**

- Michael Barr and Charles Wells Triples, Toposes and Theories
- Wim Blok and Bjarni Jónsson Algebraic structures for logic (Lecture notes)
- Peter Burmeister Lecture Notes on Universal Algebra: Many-sorted partial algebras
- Peter Burmeister A Model Theoretic Oriented Approach to Partial Algebras
- Stanley Burris and H.P. Sankappanavar A Course in Universal Algebra
- Ralph Freese and Ralph McKenzie Commutator Theory for Congruence Modular Varieties
- Mai Gehrke and Bjarni Jónsson Bounded Distributive Lattice Expansions
- Rob Goldblatt Algebraic Polymodal Logic: A Survey
- David Hobby and Ralph McKenzie The structure of finite algebras
- George Hutchinson Lattices and Categories of Modules Lattice theory equations and interesting lattices
- Peter Jipsen and Henry Rose Varieties of Lattices
- Keith Kearnes and Emil Kiss The Shape of Congruence Lattices
- Olga Kharlampovich and Mark Sapir Algorithmic problems in varieties
- Don Monk An introduction to cylindric set algebras
- JB Nation Notes on Lattice Theory Chapters 1-6 Chapters 7-12
- Herbert Wilf Algorithms and Complexity