East Side, West Side  
   Lecture notes by Herbert S. Wilf on generating combinatorial objects and Maple.
   http://www.cis.upenn.edu/~wilf/lecnotes.html

The Combinatorics Net  
   Maintained by Bill Chen.
   http://www.combinatorics.net/

ArXiv Front: CO Combinatorics  
   Combinatorics section of the Front for the Mathematics ArXiv.
   http://front.math.ucdavis.edu/math.CO

Enumeration of the Binary Trees  
   A note on Catalan numbers by Ivan Galkin.
   http://ulcar.uml.edu/~iag/CS/Catalan.html

The Combinatorial Object Server  
   Select a type together with specific parameter values and COS will return a list of all such combinatorial objects.
   http://www.theory.csc.uvic.ca/~cos/

Topics in Mathematics - Combinatorics  
   In the Mathematics Archive at UTK.
   http://archives.math.utk.edu/topics/combinatorics.html

Extremal Combinatorics  
   With Applications in Computer Science by Stasys Jukna.
   http://www.thi.informatik.uni-frankfurt.de/~jukna/EC_Book/

Encyclopedia of Combinatorial Structures  
   Searchable database of structures with specifications and counts.
   http://algo.inria.fr/encyclopedia/

Algebraic Combinatorics via Finite Group Actions  
   A hypertext by A. Betten, H. Fripertinger and A. Kerber.
   http://www.mathe2.uni-bayreuth.de/frib/html/book/hyl00.html

CATS: Combinatorial Algorithms Test Sets  
   Searchable index of problems, links and methodology maintained by the Association for Computing Machinery.
   http://www.jea.acm.org/CATS/

A Survey of Venn Diagrams  
   Various facts and figures about Venn diagrams by Frank Ruskey.
   http://www.combinatorics.org/Surveys/ds5/VennEJC.html

G-Systems  
   Theory of chord structures to create music through algorithms by Vladimir Ladma.
   http://www.sweb.cz/vladimir_ladma/english/music/articles/dide99.htm

Combinatorics  
   Subfields in the AMS MSC 2000 classification 05.
   http://www.ams.org/msc/05-xx.html

Combinatorial Data  
   Brendan McKay's collection of miscellaneous tables in graph6 or sparse6 format.
   http://cs.anu.edu.au/~bdm/data/

The Hyperbook of Combinatorics  
   A project to develop a hypertext on major topics in combinatorics.
   http://www.combinatorics.net/hyper/

Catalogue of Lattices  
   A catalogue of different types with applications to packing spheres by Neil Sloane and Gabriele Nebe.
   http://www.research.att.com/~njas/lattices/

The Math Forum Math Library - Combinatorics  
   Comprehensive catalog of websites relating to Combinatorics.
   http://mathforum.org/library/topics/combinatorics/

Math Pages - Combinatorics  
   About 40 "informal notes" on combinatorics by Kevin Brown.
   http://www.mathpages.com/home/icombina.htm

Generating Functions  
   Introduction to generating functions with interactive java applets by Alexander Bogomolny.
   http://www.cut-the-knot.org/blue/GeneratingFunctions.shtml

Operational Research Programming Trivia  
   Computer code for research algorithms in operational research and combinatorial optimization.
   http://www.ortrivia.com/

The Cutting Sticks Problem  
   An unsolved combinatorial problem by Frans Faase.
   http://home.planet.nl/~faase009/cutsticks.html

Combinatorial Catalogues  
   Combinatorial objects such as graphs, designs and geometries collected by Gordon Royle.
   http://www.csse.uwa.edu.au/~gordon/data.html

On-line Dictionary of Combinatorics  
   An expanding web text by Joe Fields.
   http://www.southernct.edu/~fields/comb_dic/