Links

• www.combinatorics.net
• www.graphtheory.com (in particular Graph Theory White Pages)

Bibliographic tools

• MathSciNet
• CiteSeerX
• ACM Portal
• CCSB
• Google Scholar
• ArXiv

General reference

• MathWorld
• Integer Sequences
• Google

Computational catalogues

• A compendium of NP optimization problems
• Graph Template Library
• Combinatorial Catalogues
• Combinatorial Object Server

Other combinatorial centres (deliberately incomplete)

• Cambridge, Queen Mary, LSE, British Combinatorial Committee (list of combinatorics in Britain)
• Princeton, Carnegie Mellon, DIMACS, McGill, Waterloo
• COMBSTRU, DMANET

Conference listings

• Peter Cameron's
• LSE's
• Doug West's

Miscellaneous

• The Erdos Number Project.
• For some comic relief you may wish to visit this site.